I need help!

Okay i just recently bought a use laptop. I've only had it for a month at the
most and well its doing something i've never seen before and i would really
like to know why this would be happening.

I recently discoverd that when the laptop has been on for more then 2 hours
that it will seize up and the only way you can get it to finish loading or
thinking is to tip it sideways. At first i thought maybe it was because it
got hot or something. But then i realized it wouldnt overheat with both the
fans still working perfectly.

So if anyone knows why i would have to turn it sideways for it to load. I
would really like to know. Thanks!