Computer restarts itself

[Computer_Idiot]

I have a problem of the com auto restarting itself when i play online games like DOTA and MapleStory, i dont get this problem when i just use the computer during normal usages such as surfing the web or typing documents. Can any computer expert please help me out with this problem, i cant seem to find the cause and solution for weeks. :-?

[GX1_Man]

Excessive heat, bad power supply or bad RAM are the most common causes. As we know absolutely nothing about your system it would be hard to speculate further.

[Computer_Idiot]

Opps..sorry bout that
My com:
Intel P4 2.4Ghz
Gigabyte Mainboard
512MB DDR RAM
80GB harddisk
400W Power Supply
NVIDIA GeForce FX 5200

Is there any way to check what is wrong?

[GX1_Man]

What make PSU? How old is the equipment? Are all fans turning? Have you checked your system temps?

[Computer_Idiot]

The PSU is a BST switching power supply:Model LC-B400ATX. I changed it around 6 months ago cause the previous 1 exploded.I got 1 fan working at the front of the CPU and another big fan blowing it.The com temp is at 53 degrees, is it too high?

[GX1_Man]

That sounds like an el-cheapo PSU, similar to the one that blew up. If you can, drop in a known working one and take it for a run. Free RAM test at www.memtest86.com. You may also want to remove the side panel and blow a fan directly in there and take it for a gaming run. I am assuming you have already removed the excessive dust inside the machine?

[Computer_Idiot]

Yup i got rid of the excess dust, i tried the method of opening the cover and blowing a fan directly, the com restarted again 10min into the run . How do i change the PSU? it looks stuck to the top. Is there a possiblilty of the programmes clashing with 1 another? Or the failure of the CMOS battery,cause my CMOS batt failed recently.

[GX1_Man]

http://compreviews.about.com/od/tutorials/ss/DIYPSU.htm