I am unable to boot my pc, I must try many times sometimes wait for some hours and try again to get it started. Generally after it starts it restarts at Vista startup but sometimes it works for hours without problem then restart.
Specs:
Asus M2A-VM
VData 1GB 800Mhz x 4
AMD Athlon 64 X2 5000+
Ati Radeon HD3850
Nec DVD writer
Seagate 320GB
Samsung 120GB USB
OCZ 500W
Any idea why this is happening?

Hey there and welcome to PCHF,

Is it able to boot into Safe Mode? You have to hit F8 before it gets to the Vista loading screen

Thanks for the welcoming. I am unable to boot the pc so not even the POST screen with "Asus logo" or "press delete to enter bios" so I am also unable to boot safely and when it keeps resetting it doesn't start on safe mode neither. When it starts it can start in safe and normal mode when it can't it just can't

Hmm.. Have you tried clearing your CMOS? Turn the computer off, pull out the battery on the motherboard, turn the computer on, turn it off, put the battery back in.

Yes, I tried that too.