I have an Intel Core i3 system with 250 GB HDD and 2 GB RAM, running Windows 7. My system is two years old. 

It frequently shuts down. Although the CPU light is on, the monitor displays "no signal". I'm not even able to work on it continuously for ten minutes. 

I thought it might be because of the OS and I formatted my C disk too, but that didn't help. What can I do?