Yes I have same problem when I play a game the Mem Usage is 200,000k then pc over heats and turns off. Does yours come back on straight away or do you have to wait 30 minutes before it decides to work again? I ain't had time to clean dust out atm. Btw I think Everest is what you need tells you everything you need to know about your pc.
EDIT: I've just used my Everest and this is the information I was given:
Temperatures:
Motherboard = 46C
CPU = 44C
Aux = 46C
WDC WD2000BB-98DWA0 = 44C
Cooling Fans
CPU 2136RPM
Chassis 2312RPM
Power Supply 1442RPM
Voltage Values
CPU Core 1.55V
Can anyone say if this is normal.
Thank you in advance.