Computer is on but nothing is working?

[Xzero]

Sometimes randomly my computer just goes blank, all the fans and the graphics card are all working fine, but my optical mouse and my keyboard show no signs. Nothing displays on the monitor. The lights are on in the computer and it shows that it is on. Maybe harddrive failure?

[Xzero]

Also I forgot to include it starts up again and works fine.

[Atomic Rooster]

Can you tell us more about your computer? Specifications such as CPU, motherboard, video card, etc. Brand and model if it's a prebuilt system.

[Xzero]

CPU: AMD X2 6400+
Graphics: EVGA Nvidia 9800GX2
Motherboard: ASUS M2N32 SLI- Deluxe
RAM: G-SKILL 1GBx4 DDR2 800
Power Supply: Roswell 850Watt
Harddrive: Seagate Barracuda 320GB 7200RPM SATA
Built by myself.