System sudden shutdowns

[CoolmePlatinum]

Here is my problem and maybe someone here is familiar with this and could help me: I built a computer for somebody and installed Win XP on it, the system randomly shuts down in the middle of sessions of web browsing or disc burning. These two are the main causes for the computer shutting down, while on the other hand you can play games or use Word without any harm it seems downloading from the web or torrents causes this to happen.

What happens after a random shutdown, the CPU or Hard Disc led (I'm not sure which I'll have to check) starts to blink and you can't reboot the computer, you have to power off the PSU at the back and back on to be able to boot again. I thought it might be a bad PSU but it was replaced when it died a couple of weeks ago. Now we're aiming at the built in Ethernet card.
Before I start spending money I'd like to be a little bit more sure what the problem is so I'll list the configuration of the computer:

Antec Smart Power 2.0 400W
AMD X2 3800+ AM2 stock cooling
MSI K9N Ultra-2F mobo
Asus EN7600GT passive cooling
1GB Kingston DDR2 PC5300
160GB Maxtor DiamondMax
Floppy
Chieftec case LCX-01SL-SL-B
NEC DVD burner ND-4571
Floppy
1*120mm exhaust fan at the back

On a note I have a legit copy of Windows for that computer but the license got stolen so I use a corporate version for now. I will purchase eventually a new one but need first to know if the computer will work.

Thanks.

 

[Dangman]

have you ran Memtest+ yet to see if there's any RAM problems? Google, download, burn and run Memtest+ for at least 3 hours to see if the RAM is defective. Run it for 24 hours if you want to be completely sure that the RAM isn't the problem.

 

[CoolmePlatinum]

ok i'll try that and post back here when I'm done.

Does anyone else think it might also be the PSU?

 

[digital_exhaust]

This is just a shot in the dark here but............heat...

You've got a passively cooled video card...stock cooling on the cpu....and a whopping grand total of *one* fan in that machine.... I would definitely take a look at the temps and make sure your ok there.....Good Luck!!