Computer shuts itself off!

[xilience]

Hey everyone, thanks in advance...

I have a custom built PC, whose components seemed to work fine for about a year now. A few weeks back, it began shutting off out of nowhere. I'm running a program, no connection between them, and it will shut off. The motherboard light remains on, but I cannot turn it back on without first turning off the power supply.
I tried taking everything out, unplugging all peripherals. I ran it all night last night without a problem. This morning I reconnected my 56k modem (yes I know, but it's a temporary setup) and then it started shutting off again. It happens even when I am not going online. This could be the problem, but I'm afraid it is just a coincidence.
Also, the power supply is fairly new, worked well out of the box, but that may be related as well.


Any thoughts or suggestions would be greatly appreciated.

Specs:
Abit NF7-S AMD Athlon XP 3000+ Kingston HyperX 3700 1GB
Sapphire Radeon 9600 XT 2x Samsung Spinpoint 80GB SATA
ATRIX 500W
Don't know the brand of the modem, but the modem has worked in the computer I took it out of for over three years without a problem.


Thanks again,

Frank B.

 

[thujone]

dead fan somewhere?

or just a general heat problem?

 

[HaelWho]

Temps by any chance?

 

[xilience]

 

[xilience]

**UPDATE**
I took out the modem and switched out the power supply to the one I used for nearly a year before this summer. No luck. I don't have an in Windows Temperature Monitor. Unfortunately, it will shut off quicker everytime. If I let it sit for awhile, it will actually run until the log on screen for WinXP. After the third attempt, I won't get past the WinXP
boot screen.

 

[nwo4life022]

try memtest http://www.memtest86.com to scan your memory...could be a bad memory stick

 

[Porter21]

I would say heat is ur culprit.