Need help diagnosing and fixing laptop
January 24, 2014 5:46 PM   Subscribe

I have an HP G42 14" laptop that has been intermittently failing to boot or wake up from sleep. Well, I think that's the problem. It's hard to tell because all I get is a black screen. No error messages or anything.

This problem started a few weeks ago. After a little casual googling of the problem, I kinda wrote it off as borked. Now that I'm looking for a replacement, I started trying to do a little more troubleshooting as a last ditch, and I'm getting some weird results.

When I first noticed the problem, the laptop failed to wake up from sleep. I heard the hard drive whirring, though, and the led light on the CAPS LOCK key was on and blinking. I turned it off and tried to start again, but no dice. There's no error message or anything, just a black screen and blinking lights. My initial research led me to believe that the motherboard was fried, possibly as a result of the battery being worn out. I can't remember where I found that explanation. I do know that I had been getting warning messages that the battery was not good anymore prior to the black screen event.

Today, I did a little more googling and ended up doing a hard reset (took the battery out, help the power button down for a minute, then trying to start up with just the AC cord plugged in- no battery). It did the same thing.

Then, I tried hooking it up to an external monitor, and it booted up just fine. This was with the cord plugged in and the battery in place. I let it boot up completely and sit there turned on for a while, then turned it off and tried to turn it on again. No dice. Black screen and blinking light. The light blinks once, which appears tp be an HP error code for a bad CPU.

I tried hooking it up to an external monitor again (this time one that I know doesn't work- I thought that maybe just having the cable in the VGA port would make a difference). Still a black screen, but this time the led on CAPS LOCK was solid on. I did another hard reset, then tried turning it on without the battery in place, and it came all the way on. No blinking light this time and everything appears to be working fine. I'm typing on it right now.

So. Any ideas on what might be going on? I kinda have an idea that maybe a new battery would help somehow.

posted by Shohn to Computers & Internet (5 answers total)
If it is shutting off when turned on seemingly randomly and then won't turn on immediately, but will 15 minutes later it could be that it is overheating. Replacing a fan or getting one of those cooling pads could fix the problem.

The monitor not working could simply be a loose cable. Its not hard to take a laptop apart enough to make sure the connection on the ribbon cable is strong.

If you are getting some booting (when hooked up to another monitor) your motherboard is just fine.

Generally if it is your hard drive you will get messages like no harddrive found, no operating system found. Or you will have currupted files and weird things with programs start happening.

If it is your RAM, generally you will get some sort of blue screen error as well.
posted by AlexiaSky at 6:11 PM on January 24

Even though it's not the same model, here's a list of the blinks you could get. If it's what you're talking about with the one blink deal, it's the CPU acting up. Which is definitely not good. It may be getting too hot, which is going to be either the fan, or if it's been going on long enough, the CPU may be damaged already.
posted by deezil at 6:13 PM on January 24

I didn't read the bad CPU part. That could qualify as overheating sometimes, but if your possessor is borked, you pretty much need a new computer unless you can find on e-bay your specific processor and know how to install them (which isn't hard, and is a good learning experience if the laptop is already broken) and the processor isn't welded on. You would have to google your computer to find out.
posted by AlexiaSky at 6:14 PM on January 24

First, there are a couple easy things to do to help isolate the problem before you consider taking it apart. Taking it apart is pretty easy, but I'll go into that further down.

- After leaving it off for a while, hook the monitor back up, start up the laptop, and hit whatever key it tells you to go into 'setup' mode - this is the BIOS, the program that's on the motherboard that controls the hardware and basic settings - this isn't on your hard drive, its actually on a chip on the motherboard. Many HP computer BIOS menus will have an option that shows the current temperature of the CPU. Use the arrow keys to find it, and if it has a temperature monitor, just sit and watch it for a few minutes. Does it stay at a stable temperature? Let it stay there for about 30 minutes on that screen, but check on it a couple times in between. The average CPU temperature should be around 35 degrees Celsius (about 95 degrees Fahrenheit). More info from HP about this here. If it hasn't frozen after about 30 minutes, it's possible that it's still an overheating problem, but not bad enough to show itself from a cold start and just sitting there idling. On to the next step.

- Lets check the RAM. Turn the laptop off, flip it over, and unscrew the plate on the bottom that has a picture of two little RAM chips on it - its in the dead center of the middle of the underside of the laptop. The HP service manual has helpful pictures of this on page 60. You should have two chips in there - if you only have one chip, close it up and skip this step. Take one of the chips out, flip the laptop back over, and try starting it up again. If it starts up, let it load, and repeat this a few times - it will run slower, but it may be that one of your ram chips could be starting to go bad. If the problem remains, turn it off and take the other one out, put the other chip you took out earlier back in, and see if there is a difference. If this fixes it and is stable after several restarts and a few hours of use, you may just need to replace that bad ram chip, which should be less than $50 or so. The startup problems would have been from the motherboard checking the ram before it turned on the screen - bad ram can pass these tests sometimes, so this would explain why it's intermittent. The tricky part is that there is a very small chance that both ram chips are going bad, but that is a pretty rare thing to happen judging by how your laptop is behaving.

- So you've taken it's temperature, checked for bad ram, but the thing still is not telling you what's wrong. If you're up for a little adventure, and willing to spend some money on some easily available parts, there's really only two things that would need replacing. That laptop does not look too complicated to get inside, and you can watch the whole video of the take-apart for the G42 right here.

What you'll need:

- a set of small phillips head screwdrivers of various sizes.
- Thermal paste - available from any computer store for under $10. I recommend Arctic Silver brand.
- A compatible motherboard (about $50-100 on ebay - see note below)
- A new heat sink/fan assembly (about $12 used, $30 new on ebay - see note below)
- A grounding strap - ($2, goes around your wrist and prevents static electricity in your body from ruining the motherboard)

Now the thing with this is, is that there are several kinds of motherboards and each only works with a specific heatsink/fan assembly, so you have to make sure you're buying the right ones. If you take the laptop apart, HP has been nice enough to put a sticker on each of them telling you the correct part number for the replacements. However, this means you'll have to either take it apart twice, (once to check the stickers, once to replace the parts) or you'll have to leave it in pieces until the parts arrive. I strongly suggest going with doing it twice - a lot can happen in a few days - screws get lost, things get knocked over, etc. I also recommend changing both parts at the same time - the fan and heat sink are cheap, and it's worth it to only have to go through this once.

That HP service manual I linked earlier has almost all the steps and diagrams you will need to swap out the parts - around page 91. The only other thing I can add is check out at least two or three youtube videos about how to properly apply thermal paste before you attach the heat sink to the CPU. It's the most important part of the process to get right. It's not complicated at all, but there is a certain way you have to do it to make it do its job right. Here is a video showing the process on the G62 laptop, and it should be just about the same process for you as the motherboards for some versions are interchangeable.

Wow, that ended up being longer than I expected. Hopefully this should be helpful in getting everything back up and running. As I was looking up info on this, most people seemed to say that it was the motherboard and fan that needed replacing. Some were able to fix it just by removing and re-applying the thermal paste, and their startup problems went away. In any case, although this process can sound complicated and a little daunting if this is your first time, it's really not that bad. Just make sure you keep track of your screws, and use a grounding strap, and you'll be fine.
posted by chambers at 8:04 PM on January 24

Well, it doesn't appear to be the memory- I did the test as described by chambers, and there was no difference. At this point, it's worth it to start taking the thing apart to see what I can figure out. Thanks all for your help!
posted by Shohn at 4:38 PM on January 28

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