Computer randomly crashes and powers off with no display signal

My PC automatically powers off after some minutes of normal use (opening OS, MS Word typing,
Internet Explorer surfing), then suddenly my screen turns black and displays "no signal input".
Could there be a problem with my operating system or is it a hardware issue?
I suspect that it could be my power supply.
Here are my computer specs:
Processor: AMD Athlon 7750
Mobo: Emaxx 780G-PRO
Memory: 2GB DDRII-800 (Generic, no brand)
Video: Nvidia 9600GT 512MB
HDD: WD 250GB Sata II
Supply: 350 Watts (Generic, "Geniepower" brand)
