Yea.. ok he installs Windows 7 and you ask him about dust in the fan. lol.
9 times out of 10 this is a drivers update issue. This happens quite frequently on HP Pavilions.
Either you need to update your BIOs, or the new video card driver windows 7 installed is causing it to overheat and crash.
This has been an issue with my HP Pavilions since I bought it a year ago, anytime Windows update tried to update the video card drivers, immediately the laptop would over heat and begin shutting down without saving work. Returned the computer 3 times until the warranty ran out, then HP wanted a ridiculous amount of money to repair something they did not repair the first three times.
I recommend try to roll back to a previous video driver from before the Windows 7 install. If that does not work, you may not be able to resolve the issue unless you revert back to previous OS.
I just upgraded to Windows 7 last night, and almost immediately this laptop began overheating and crashing as well.