Working on a friends computer

it loads in cpu-z as a ecs m922 but the m922 is made by pc chips, anyways, recently the office it is in is kept around 64 degrees F, and the cpu has been locking up, and i believe reaching temps as high as 91c, the fan looks good and is working, but i air dusted the entire case no dust whats so ever, no oc'ing on this machine, any ideas what could be causeing the constant overheating?
edit
also, it is a p4 1.8 with stock cooling, i saw that the thermal paste is old and bad, so i will replace it, but the stock cooling has this pad it looks like on it, should i remove it? and use as5 only?

I would clean the pad off as best you can, idealy with no pad left. And then use as5. The case could have been jarred which caused the heatsink to not make good contact. If the office is that cool, there is no way that 91C should happen. How are the intakes?

ok did it, but still raising in temps maybe for some reason its not enough contact.. hmm

Edit
No intakes, but it's worked for over a year now.

also i think its a pc chips m922lr thats what thre bios says...