My computer stopped working!
April 3, 2015 11:20 AM   Subscribe

I just got home from 6 weeks of holidays, moved house, reassembled my desktop and when I turn it on the monitor doesn't get a signal. Is the most likely cause a motherboard failure?

I've tried removing the video card and using the on board without success.

I've tried resetting the cmos.

I've moved the RAM dimms around and alternated removing them with trying different slots and the only difference is either the computer will fail to turn on at all or will turn on for a few seconds and loop through a reset every 5 seconds or so.

At no point does the monitor get a signal. There is no beeping but the fans and hdds all turn on and the lights on the case turn on.

I did have a problem with the computer failing to boot previously but just before i was about to start working out what was wrong it randomly turned on, i flashed the bios and it worked until now.

I unfortunately don't have spare components to try a different cpu or mobo.

Does it sound like the best solution is to buy a new mobo or am i missing something?

Oh, the usb keyboard isn't getting power although i can charge my phone through the usb ports, as well as use the monitor settings so I dont think its a monitor issue.
posted by Silentgoldfish to Computers & Internet (5 answers total)
Did you try using a different cable to connect the monitor to your computer?
posted by Hermione Granger at 11:23 AM on April 3, 2015

Sounds like it could be the CPU, MB, or PSU. Have you tried re-seating the CPU? (be sure to re-apply thermal paste if it is crusty).

When you look at your MB, are you seeing any capacitors with bulging caps? Do you have a multimeter?

The fact that you're not hearing the normal beeps makes me suspect it's not memory or other peripherals....but you can also try booting without any devices plugged into the MB.
posted by samsara at 11:34 AM on April 3, 2015

Check and if possible swap the cable. If it's VGA, check the pins.

Does your motherboard have on-board video? Try that-- maybe your video card is kaput.

Try taking the monitor (with or without cable) to another computer and see if the monitor gets a signal from a different computer.

Is the monitor searching through its inputs automatically? Maybe it's just the input setting on the monitor was reset and it's waiting for a signal on the wrong connection.

If the USB issue and the monitor issue are related, that says motherboard. Since you moved, it means something got jarred out of place, so you'll have to check and re-seat everything on the mobo. Also check for anything conductive that's might be crossing wires.

How do you know the keyboard's not getting power-- is it possible some of the powered features you're expecting, like backlighting, are just turned off? Watch the keyboard's Capslock/Numlock lights when booting the machine-- they should flash at least once. Check the keyboard connector pins aren't overtly damaged.
posted by Sunburnt at 11:45 AM on April 3, 2015

Best answer: Here are the tests I'd do if somebody brought that to me to fix.

1. Disconnect the mains cable, press and hold the power button to encourage the PSU's internal capacitors to discharge, then wait 15 seconds.

2. Unplug everything from the mobo - RAM, video cards, SATA cables, audio, CMOS battery, everything - except the CPU, the power cables and the mobo speaker (if that's not built onto the board).

3. Fit a new CMOS battery.

4. Reconnect the mains cable, press the power button, and listen for the expected POST failure beep: I have never seen a functioning desktop mobo that won't beep in some way after these steps.

If there's no beep: repeat step 1, then disassemble the CPU cooler assembly, clean off all the old thermal gunk, remove the CPU, blow out the CPU socket with compressed air, replace the CPU and refit the cooler with new thermal paste (using Arctic Silver's recommended application method for the specific Intel or AMD CPU concerned) before trying again from step 4.

If still no beep: switch the CPU into a known-working mobo with a known-working PSU (power supply unit) and try again, to see if the fault follows the CPU or stays with the mobo+PSU. I have yet to damage a mobo+PSU by switching in a faulty CPU, but I have definitely destroyed CPUs by trying them in faulty mobo+PSU combinations; this is why I test the suspect CPU in a known-good mobo rather than the other way around.

If the CPU starts correctly in a known-good mobo with a known-good PSU, next test is to restore it to the suspect mobo, then power that up using a known-good PSU. If that works: replace the faulty PC's PSU and verify that I can now get a POST beep. If not: replace the faulty PC's mobo and verify that I can now get a POST beep.

In most cases there will be a POST beep at step 4, and the CPU, PSU and mobo switching dance won't be necessary. But having got a beep out of the thing by whatever means, look up the meanings of the beep codes for that particular mobo online and carry on:

5. If the mobo appears to have been exposed to cigarette smoke, clean out its PCI, PCIE and RAM slots with a non-lubricating spray contact cleaner like CRC CO followed by a good blow out with compressed air. If not, just the compressed air will do.

6. Carefully examine the edge connector on one of the RAM DIMMs. If there is even the slightest discolouration, polish the gold contacts using a white pencil eraser (not an ink eraser; too abrasive), being very careful not to dislodge any of the tiny surface-mount components typically soldered to the board near the connector. Follow up with a spray of CO and a burst of compressed air to dislodge any leftover tiny rubber crumbs (this whole process gets done on an ESD-safe mat well away from the mobo so that none of those crumbs end up lodged in its slots).

7. Repeat step 1, refit one RAM DIMM in the slot nearest the CPU, repeat step 4, and verify that the POST beep still occurs and that the beep code is now either the expected successful-start one or the missing-video-card one for boards without inbuilt video.

If the beep code doesn't change, diagnose a faulty RAM DIMM and repeat from step 6 for each of the remaining DIMMs if any.

8. If there's no inbuilt video, examine and if necessary clean the graphics card's edge connector per step 6, then try to get a successful-start POST beep after refitting it per step 7. Can't? Diagnose a faulty GPU card.

9. Having obtained a successful-start POST beep, systematically plug things back in (doing step 1 before, and step 4 after): video monitor cable, keyboard+mouse, remaining RAM DIMMs, SATA cables, audio cables and whatever else, verifying expected behaviour at each step.
posted by flabdablet at 2:15 AM on April 4, 2015 [3 favorites]

It would be interesting to know the result of your fault-finding.
posted by flabdablet at 7:49 PM on April 6, 2015

« Older What happens if you exceed your limit of social...   |   How to design a bet? Newer »
This thread is closed to new comments.