PC shutting down when running virus or malware scans

I noticed yesterday that my computer was running slow and a huge % of the processor was being used when nothing much was happening. When I tried running my audio program (cubase) the computer really struggled and the sound was breaking up. I closed the program and did a few searches to identify the problem. The first response was to do a virus/malware check, so I did, but my computer just started shutting down about 1/3 of the way through the check. It will start up again OK, but if I try another scan it closes down.

Firstly, I restored my system to point around 10 days ago when everything was running OK, but the scan problem still prevailed.

I then did a disk cleanup, and deleted temp files, temp internet files, program downloads, and the recycle bin. Problem was still there.

I then attempted a disk error check, however the computer shut down half way through this process as well.

I am really stuck as to what to try next. I have no idea if this is a hardware or software/virus issue. My computer will start up and run for a while, but then the Processor use gets very high again, and it's impossible to run most programs. It will then automatically power down.

Any help or advice would be much appreciated.

James

I have included some specs below:

Intel i3 processor

4GB RAM

1TB HDD C: 320GB with OS E: file storage

Windows 7 Ultimate

Avast Free Home antivirus

via Bleeping Computer Last 20 Posts http://www.bleepingcomputer.com/forums/t/509109/pc-shutting-down-when-running-virus-or-malware-scans/