Windows 7: PC suffering various issues

My pc is suffering from various issues and I'm not sure what the cause is.
I think my harddrive, C:, is failing.
I've come to this conculsion based on running a seagate disk tools DST on the harddrive and it failed.
So Seagate is sending me another drive and I will replace the old one. My concern is that the seagate has a tool that allows you to clone one drive to another. However, my pc likes to reboot itself whenever I do a malware/virus scan on the C drive.

I've tried numerous online virus scanners and my pc chugs along then decides to reboot itself.
I even attempted to copy my c: drive to an external drive and it eventually attempted to reboot itself.

The latest issue is that I wanted to see the properties of my C drive, so I right clicked on the drive, selected properties and now all I get is the little circle spinning round and round. It used to be an hour glass for busy in xp/vista, now its this annoying circle.
My disk activity light is blinking indicating that there is disk activity ocurring.

Can someone please help.

Thank you,

Btw, this is windows 7 ultimate x64 build.