[ale] Urgent, hardware problem

[Tri]

I have an atx motherboard and an atx powersupply. In the last week my
computer has been randomly shutting itself off, and I have trouble
getting it to turn back on. On my system I have two power switches. One
of them is connected to the power supply and one of them is connected to
the motherboard. When it shuts off the computer doesn't report any
errors or any sign that anything is wrong. When it shuts off I wait a
minute and press the power button connected to the motherboard, and
nothing happens. So I switch off the power button on the power supply
and switch it back on. When I do this I see the power light flash on for
a second and turn off. I repeat switching it off and switching back on
for a couple of times and then it finally turns on. The bios reports no
errors, the harddrive is ok, memory is ok, basicaly it says everything
is ok, except linux complains that the partition wasn't cleanly
unmounted, which is expected. This went on for a week or so and started
happening more frequently. Now I can't get it to turn back on. The light
still flashes for a second, but it still does nothing. I've checked all
the wire connections inside the computer and everything checked out ok.
I don't think this is software related since it happens in windows too.
I don't think it's the motherboard's problem since the bios says
everythings ok and when it turns on it behaves as if everythings ok.
I've eliminated every possibility except the power supply, but I'm not
sure. Do you have any ideas on what is wrong? I was tempted to open the
power supply box but a warning sticker on it told me not to. I really
need to get my computer back up. 
Any Ideas?

Thanks for any help,
Tri

PS. I will make a summary of the ISP postings but as you can see my
computer is down. I switched to atlnet, and I have found out that it is
much better. I am typing this on my old Packard Bell computer.(Can't
believe that it still works)