Periodic laptop lock-up during heavy processes

Hey guys!

I'm having a problem with my studio 17 notebook. The machine is about a year and a half old (so conveniently passed warranty :emotion-6: ) but the problem only started to occur no longer than two months ago. The problem is this: whenever I do something mildly heavy on system resources, such as playing a game, I'll be able to play for about 30-60mins just fine, but after that time the computer will almost completely freeze. Ingame the fps will drop to something around 1, and if I can load up task manager my cpu total is shown at 100%. After about 5 mins of this lockup, everything then resumes fine and I can play on. But then in about another 30mins it happens all other again, and so on, and so on. I have actually recently reformatted my computer in an attempt to fix it, but it hasn't helped. So it's definitely not a virus. 

Some other info: When the freezes occur, I can look at the processes section of the task manager and the total cpu (bottom left) says 100% as I said. However if I count up all the processes cpu, it barely scratches that number. Often the highest cpu user is the task manager itself. This issue seems to occur on pretty much every game I play. The only one it doesn't is Total Annihilation, which is 14 years old.

I had my suspicions it was a heating issue, so I downloaded a program to manually manage my fans, called I8kfanGUI64. I forced it to put all my fans at max speed to see if it would help. It didn't. At about the time the freeze would normally occur, there was a click somewhere inside the laptop and it switched off. Not shut down, just instantly switched off. Obviously I didn't try that again...

Sorry for the long post, and if anyone has any ideas they would be much appreciated, I really don't know what to do.

Thanks! :emotion-1:

Specs:

Studio 1745

4gb memory

220gb HD

Pentium Dual-Core T4300 2.10GHz

ATI Mobility Radeon HD 4650

IDT High Definition Audio

A02 BIOS

Windows 7 home premium 64-bit

It's also wide screen if it matters, resolution is 1600x900