Format your computer and install fresh OS. If it is not restarting after installing OS, then your operating system is the problem. Maybe your OS is infected by a virus.

I've had this exact problem before, same OS and brand. The problem for me was that for some reason the fan was not keeping my motherboard cool enough. Most computers come with a safety feature that will automatically SHUT DOWN (not put to sleep) your computer if it over heats. May want to look into buying an alternate computer fan from best buy or radioshack for under 20 bucks if that seems to be the problem.