Random PC freeze-ups, hardware damage?

Hi all!
Sorry for having to ask this, but I am really at a loss.

So, I've got a bit of a problem and it's really starting to frustrate me.
Sometimes, my computer will randomly freeze up. I don't get an error message or bsod,... nothing. The only thing i can do is manually shutting it down (holding in power button for 5 sec). The freezes seem to become more frequent, because i can't really go through a session without it freezes. And it doesn't just freeze when running heavy games but also just when idle on the desktop. I have already run mem86 although it freezed after 3 min so i used windiag (bios) and that didn't turn up anything. I've cleaned out the case of dust and reseated the gpu, cpu and ram sticks (same mhz).
The temperatures are not the problem, cpu and gpu don't go above 30°C when idle and not above 40.
(It's cold in this room so..)
I also did a full pc clean-up, so i deleted the registry stuff, defragmented, freed up hard drive space, updated all the drivers (even the bios), really the lot...
I'm kinda at a loss here. I looked up alot of fora and alot of people have a similair problem. But pretty much a different answer to all of em (or noone).
My only guess now is that some hardware component is broken or something, maybe the cpu?

Specs: Fujitsu Siemens Scaleo P
Power Supply: (think this might be the problem?)
Size PS2
Voltage 200 - 240V
Frequency 50 – 60 Hz
Max. Output up to 350W
PCU: Intel core 2 Q6600 quad core 2,4 ghz.
Video card: ATI Radeon 5750 HD (1gb)
RAM: 4gb DDR2
Motherboard: Fujitsu Siemens: MS-7379VP (AMI-BIOS)
Chipset: Intel P35/G33/G31
OS: Windows XP

Thanks in advance to anyone willing to take a look, I'll be forever gratefull!
 
Is XP fully updated to Service Pack 3 and what is the make and model (wattage) of the power supply?
 
Is XP fully updated to Service Pack 3 and what is the make and model (wattage) of the power supply?

Yes it is.
The power supply is an FSP 400-60HLN: It says on the battery 152 Watt max. Although i find that kinda hard to believe, since the description says it's 350 Watts?
EDIT: Scratch that, after a closer look it said 152 Watt continuous and won't exceed 400 Watt max.
 
Nono, sorry, battery wasn't really a right term. I just looked on the power supply for the info, so i opened the case from my desktop. (i don't have a box/case something that runs through my power cable) just a regular cable (from Longwell).
Hope this all doesn't make me sound stupid ':-|
 
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