Thanks for the reply. I ran FurMark first to stress my graphics card. It got to 81 degrees and it didn't look like it was going to go any higher so I exited the application, things seemed fine for about a minute and then the screen froze in a similar fashion to what I had described in my previous post. I'm going to do a fresh install of NVIDIA drivers and stress it again.
EDIT: Did a fresh clean install and ran the FurMark again to around 80 degrees and it didn't freeze. I played Runescape again and not even 5 minutes into the game it froze and needed to be restarted manually. Event Viewer came up with these.
The previous system shutdown at 2:37:43 PM on 17/02/2011 was unexpected.
"Event 41, Kernal-Power"
The system has rebooted without cleanly shutting down first. This error could be caused if the system stopped responding, crashed, or lost power unexpectedly.
"Event 10016, DistributedCOM"
The application-specific permission settings do not grant Local Launch permission for the COM Server application with CLSID
to the user NT AUTHORITY\SYSTEM SID (S-1-5-18) from address LocalHost (Using LRPC). This security permission can be modified using the Component Services administrative tool.