System restarts unexpectedly

[sholay]

System Config

p4 3ghz 800FSB 1mb L2 cache (prescott)
Asus P4P800-VM
512mb RAM
Windows Xp SP1

The system restarts unexpectedly after i work for 30 min or so,
sometimes it restarts immediately on booting.

I have loaded the default setting in bios.

I have one extra fan.The mobo and processor temperature is aroung
50 deg.I don't think it is a problem of overheating.

what could be the problem

[Santosh Halemani]

Put specifications of ur power supply or check for the windows error reporting center. U will find it in my computer>right click> then serch for error reporting. Some times the system is to restart when critical error occurs. Try it . Good luck!

[sholay]

I am using mercury 350W smps

[suhasingale]

First off all chek wether ur CPU fan is working properly or not. Ensure that u have not removed the thermal paste on thw Heat Sink wich comes wid it. If the same problem exists den chek for the Ram, wen the PC restarts immediately turn it off and touch the RAM wether it's too hot or normal. if its too hot then replace it ASAP if under warranty.
Lastly i wud like to recommend a 400W SMPS for Asus boards.