I turned on one of my desktop computers and it wouldn’t even boot to the BIOS screen. Black screen, not even a signal detected. The lights and fans came on, as well as the HD and DVD drive lights. I tried leaving it for a while and then pushing the keys that would make it shut down, but nothing happened, it’s not booting at all. Even tried a different monitor, but still no signal detected.

A funny thing is that when I would press the button, the computer would turn on (fans and lights, that is) and then go off by itself after five seconds—and then after having been off for 3 seconds it would turn back on again by itself with still ntohing showing up on any screen.

So—motherboard or power supply? I figure it’s the Motherboard, but in case it isn’t, I can perhaps benefit from someone’s experience here…

Well, if no POST at all then it could be CPU, motherboard, bad memory, or possibly the PSU. It’s not likely the PSU since fans are spinning so it could be the other 3 items. One thing to try is to clear the BIOS. This is usually accomplished by moving a jumper cap for a few seconds and then putting it back (while the system is off and unplugged). This will set the system to default settings and might allow you back into the BIOS settings.

If not, then it’s likely a hardware problem. You can try removing memory sticks (testing them one at a time) as well to see if one of those is the culprit. If it’s the CPU or motherboard it will be difficult to test unless you have access to another CPU and motherboard for testing.

yea, what groovy said, basically just trial and error with your different componets,  do you have the speaker connected to the motherboard? does it make any sounds?

UPDATE:

I finally got around to trying it out with a differfent PSU. Same problem. RAM also makes no difference.

It really strikes me as odd that the computer goes on (lights up & fans) for 3 seconds, then back off for a second and then turns on and stays on until I force shutdown. I wonder, what causes that? Does that sympton ring a bell with anybody?

could it be a virus which has written junk into the BIOS? Newer motherboards come with 2 BIOS chips to take care of such situations. How old is your comp.?

I bought the motherboard brand new in Taiwan a year and a half ago. The CPU is an AMD 2200 XP+...

Now that I think of it, this computer is never hooked up to the internet, as I use it only for music mixing. It is not on the network at all. So I guess that rules out any viruses—I hope!

Was/is the cooling fan working on the CPU? Is it extremely hot and cramped where the computer is? Was/is the computer hooked up on the same circuit with musical equipment or a laser printer? Does your area/building have a history of electrical problems and power dips? As gr00vy said, it’s most likely a bad CPU or mobo killed by being on a circuit with too much load or power dips or the CPU overheated.