MOBO or PSU failure? (sometimes doesn't boot, sometimes does)

dimitree

Commendable
Dec 27, 2016
2
0
1,510
Hello everyone,
I have this desktop configuration that worked for many time:

MB: Asus P5Q SE Plus
CPU: Intel Q8200 (2,33 GHz)
RAM DDR2 800MhZ 4gB
GPU: NVIDIA GeForce GT 220

then it started to give me this problem:

when I press the power button, it briefly starts up, but before even reaching the BIOS, so after about 1 second, it shuts down for some seconds, then it restarts automatically but, still not reaching the BIOS, keeps on restarting.
There is not beeping (the buzzer/speaker is connected and working).
Then, if I unplug the power cord for something like 10 seconds, plug it again, it powers up fine: I can hear the beep, see the ASUS messages on the screen, and I can finally reach my Windows installation.
Sometimes this procedure works, sometimes I have to make it twice or more.
In the end, I can always start my OS, but it is really annoying to do so every time.
Also, I noticed that this procedure only works if I don't have a battery plugged in the motherboard. If there is a battery (even a fresh one), it won't boot with "my procedure".
Since I can't use a battery, the BIOS settings get their default values every time I boot, so every time in Window I have the date set to 2002 (another annyoing thing).
Also, if there are many USB devices plugged at startup, you have less chances that it will boot at the first try.

I did the following, but none of them helped:
- Cleared the CMOS following the ASUS procedure
- Removed the GPU
- Removed the 2x RAM (one at time first, then both). Also tested them with memtest and they are fine.
- Removed the HDD, DVD-Drive, USB devices.

When I'm finally in Windows, I noticed that I cannot plug many USB devices, if I do, some of them will randomly disconnect (for example, if I plug my external HDD, it will work for some seconds, then disconnect, but it works fine on other PCs).

So it may be a PSU failure that can't supply enough juice at startup? Or do you think it is the motherboard?
I'm more biased toward the PSU failure, since I can boot the system after a while, but before throwing money for this machine, I'd like to hear some suggestions.

Thanks
Dimitri