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March 13, 2009 7:40 AM

Why won't my computer post?

About a year ago I built this computer. It died a month ago, and I thought it was the video card. The card was replaced under warranty. I popped the new card in the system this morning and was disappointed to find that it's still not posting.

When I press the power button, the fans spin, and everything seems normal for about the first 3-4 seconds, then it just shuts off before a video signal is ever sent to the display. About 4 seconds later, it starts again, fans spin for 3-4 seconds, and then it dies. This repeats indefinitely until I kill the power by flipping the master switch on the back of the power supply.

My next guess is that it's the motherboard (GIGABYTE GA-P35-DS3L LGA 775 Intel P35 ATX Intel Motherboard ) or processor, but I'm not sure how to troubleshoot that problem. It looks like all the cables are connected.

Any thoughts?

posted by spikeleemajortomdickandharryconnickjrmints to Computers & Internet (12 answers total)

Make sure that when you popped in the new vid card you didn't dislodge the heatsink from the CPU, could be a thermal shutdown (happened to me)
posted by zeoslap at 7:52 AM on March 13, 2009

Response by poster: It's acting like a thermal shutdown, but I checked to make sure the heatsink was secured to the top of the processor. It's a very beefy heatsink/fan combo (this one).
posted by spikeleemajortomdickandharryconnickjrmints at 7:56 AM on March 13, 2009

I've got that heatsink. Its tremendous size makes it easy to knock the damn thing....you might consider taking it off, cleanin both it and the processor, and putting a fresh dab of heat sink on them.
posted by notsnot at 8:02 AM on March 13, 2009

It should take a CPU rather longer than 4 seconds to reach shutdown temperature even with no heatsink at all. Also, if the problem was CPU heat, I'd expect to see the first cycle of switch on/shutdown take rather longer than the rest. Try starting the box with no RAM and no video card in it, and see if you get an appropriate beep code. If not, try a different power supply. I've seen about five times as many failed power supplies as failed motherboards.
posted by flabdablet's sock puppet at 8:15 AM on March 13, 2009 [2 favorites]

Do you overclock? I have an almost identical MB get this from time-to-time due to overclocking. However, it had nothing to do with temps as my CPU runs cool, but rather my processor just couldn't handle the extra juice I was giving it. However, after about 3 cycles, the BIOS reverts back to default.

It doesn't sound like a video card problem. Your computer would still post without one.
posted by jmd82 at 8:19 AM on March 13, 2009

I second flabdablet's's suggestion; this sounds like a power supply issue. Make sure it produces the right wattage to handle all your components, then try replacing it.
posted by TimeTravelSpeed at 8:29 AM on March 13, 2009

I have a PSU that behaves exactly like this when I forget to spread the load between two 12V rails, because one of them has gotten somewhat weaker over time. But, yeah, I will put money down that this is your PSU. If you swap the PSU and it does the same thing, I'll paypal you a buck.
posted by majick at 8:54 AM on March 13, 2009

Consider investing in a Port 80h card, if these steps fail. These are small PCI (and sometimes PCI/ISA) cards which are slotted into the motherboard. When you boot the machine, it will display, using LEDs, a code which you can look up. This code can tell you where your boot process stopped.
posted by adipocere at 10:04 AM on March 13, 2009 [1 favorite]

When I build system, I get the on/off deal a lot. It's not CPU overheating.

Some component isn't setup properly. I'd try reseating everything, CPU, RAM, GPU. Also, clear your CMOS with the jumper on the motherboard and you should be fine.
posted by wongcorgi at 10:57 AM on March 13, 2009

Response by poster: I reseated everything and cleared the CMOS jumper and it didn't change anything. I'll try to find a power supply this weekend and swap it out to see if that solves anything.
posted by spikeleemajortomdickandharryconnickjrmints at 12:46 PM on March 13, 2009

The symptoms you enumerated could point to all sorts of hardware failure. In my experience the culprits are in the following order from most to least likely:
1. PSU
2. Motherboard
3. RAM
4. CPU
5. Peripherals (Video, Sound, etc)


However, before you replace items in that order, troubleshoot by:
1. Pull everything from case including CPU and all cards (mouse and keyboard too).
2. Put back only necessary components.
3. See if you get POST.
4. If no post, investigate 1-5 above.
posted by |n$eCur3 at 12:46 PM on March 13, 2009

Every single time I've had a machine that did something like this, it's been due to a bad PSU.
posted by Caviar at 5:30 PM on March 14, 2009 [1 favorite]