machine switching off randomly

im running a p4 3e with asus p4c800-e motherboard, 512 ram, maxtor 120gb hd ata 133, gigabyte nvidia fx5900xt and a 400w psu all in Thermaltake tsunami dream case with 3 fans. CPU temps around 49c , 12 rail @ 11.6 volts. All ok while surfing the net , downloading files and general usage but when attempting online games such as UT2004 or Joint ops typhoon rising the machine shuts down and cannot be reset with the power switch but needs to have the power to the psu disconnected to restart, this does not happen at any particular times it can be 5secs into a game or 5 mins or 5 hours there is no pattern. the latest bios has been installed memory usage is fairly high it can be over 85% while online and playing.

 

what psu are you using, and is the wattage high enough for that system spec? should be at least 400W with what you have there, so that could be the problem, it might not be able to handle such powerful games like UT2004...

 

if you have a generic psu in there its best you switch that one out for a named 350w at least.

 

the power supply although not a named brand is rated at 400watts , the other thing is that if i disconect the power from the mother board i can restart the machine and do not need to disconnect the power supply