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Powers up for 2 secs, then powers down - repeat...

Last response: in Systems
May 24, 2010 7:49:49 AM

Hi guys

Having a big problem with my computer. Built it a couple of months ago and it has been running perfectly since then until today. Turned it on today, the computer powered up, stayed on for a second or two, then powered down. About 5 seconds later, it powers up, then down again. This continues until the system is switched off at the wall or PSU. It doesn't get as far as the POST.

System Specs:
Core i5 750
Gigabyte GA-55HM-UD2H
4GB DDR3 Ram
Can't think of the graphics card off the top of my head

I tried breadboarding the computer with only the CPU and fan, one stick of RAM, and the video card installed. The same problem occurs.

Also done the following:
- Power button - took it out and tried booting the computer by shorting the pins
- Reset CMOS
- Checked the 4 pin CPU power connector
- Checked the CPU fan - it spins, and there is thermal paste (although it is the factory tape)

As far as I can see, it seems to be either a problem with the CPU/Heatsink, the motherboard or the PSU. The question now is, have I missed something, and if not, which is it more likely to be?

Anyhow, would greatly appreciate any thoughts you have on the matter. Cheers.
a b B Homebuilt system
May 24, 2010 5:49:46 PM

Sounds like something died. You're gonna have to just swap out components with ones known to work to test.

Do PSU, RAM and GPU first as they're the easiert to swap. Then CPU and MOBO as those are more difficult to test.

Also make sure you've read this thread
a c 122 B Homebuilt system
May 24, 2010 6:57:13 PM

What kind of PSU? That's what I would look at first.
Related resources
a b B Homebuilt system
May 24, 2010 8:08:52 PM

PSU problem would be my first guess. Is it like this?

That failing, I've also seen things like this happen when the motherboard just can't figure out the power management situation properly. A lot of times, that'll happen if it doesn't like a particular voltage setting. But if you've already done a CMOS reset, that shouldn't be an issue. Check out the power supply first.
May 25, 2010 4:06:40 AM

Similar to that video capt_taco, but it restarts by itself and won't stop until I pull the plug.

Tried a new PSU, no change. Wondering what next - motherboard or CPU? I know it's not the GPU and the RAM. Is it worth replacing the thermal paste between the CPU and heatsink first?