Randon Crashes

I have just built a sys. for the first time. It runs good until it seems to shut down. The screen goes black and the power light turns orange(17" Sony Trinitron) I reset the comp. and it runs normal for awhile. HELP!

MSI KT8 Neo2-motherboard
AMD Athlon 3500+
1g ram
120 g seagate hd
9800 pro

Check the power supply first, could be underpowered for this system. Also check all the power connectors too, reseat them on the motherboard and all the drives just in case.

Also, could be a thermal issue with the CPU, be sure the heatsink/fan is mounted properly, it doesn't hurt to reseat this as well

Thanks for the tips i will look into the power supply
as for the cpu temp. it runs around 42-48 degrees cels.