Hi,
I just spent ALOT of time resolving this very issue with an HP Pavilion A1010Y.
It turned out to be the following:
The Heatsink frame had cracked and 2 of the 4 screws that hold the Heatsink to the CPU for cooling, weren't doing their job.
Also, NO Thermal Paste remained.
I replaced the Heatsink, Fan and Thermal Paste and Now it works fine.
Sounds like yours is overheating, just like the one I just fixed.
Good Luck
Phil