What are all the reasons for random reboots or freezing ?

I have a PC that keeps freezing or randomly reboots itself. It usually does that in demanding games like BF2 or WoW and the likes, I've checked CPU temperature after the reboots and its usually normal. I've replaced the PSU and CPU fan but nothing changed. I tried making better ventilation for the whole PC but there doesn't seem to be much improvement. Swapped out RAM but still the same issues. I've exhausted all ideas so help please ?

System Specs:
CPU: 2.6GHZ, 512kb cache, 800 FSB
HDD: 120 GBs Maxtor
RAM: 512mbs
VGA: Geforce 6600 256mbs
OS: Windows Xp Pro + Sp2
M.B: Asus P4PE-X

So any ideas guys ?

 

the ram is quite sufficient for gaming actually, it allows for most of the games to play fast enough on high settings with little slow downs, ofcourse you can't be running too much stuff in the background. I'm planning to increase it in the future but I doubt RAM has anything to do with the restarts.

As for the event manager, I checked there and there doesn't seem to be anything major, just a handful of errors about my cdrom (cause I removed it) or when applications sometimes freeze and have to be end tasked.

 

no BSOD's appear, its just a random restart or freeze. So no useful error code there

There are many occasions when this happens, but I've found that it frequently happens when I try to host a server for BF2 and get other PCs in my LAN to log in it, not too long after that it restarts.

 

well, I've replaced both, they couldn't have gone south again so fast.

Btw, do you know of any reliable RAM testing programs ?

 

random freezes and reboots is a classic symptom of a power supply ready to fail.

 

some are caused by viruses and spywares

 

I'm pretty sure I don't have any viruses or spyware at all.

I thought so too, I even went out and bought a new PSU but nothing changed.

 

here it is

 

so hows this related to the reboot ? And what exactly causes this ? This PC is a limited user account so there are some group policy limitations in place. The firewall & network do work properly so I'm not sure what this error really indicates.

 

well, I finally caught it giving a BSOD with "driver_irql_not_less_or_equal", I've been told that it has given some BSODs before but I was never there to see them. They also don't show up in the Event Viewer, or any reports of saving the memory dumps.

The culprit driver was reported to be portcls.sys , any ideas ?