Hi there,
Overheating is a major issue with computers. If you could get ahold of your friend, ask him if he put some
CPU thermo gel (or thermal paste, something like that) between the
CPU and the heatsink with the fan. Then check if all your fans are clean of dirt, do that for every single fan in your computer, take a soft bristle brush or one of those air cans and take your computer outside and give it a good clean.
See if you can add any more case fans, I've got 5 in my case. Before you do that, open up your side panel and put a fan poiting into it (a big fan, as in a table top fan or something) and make it blow on "High" into your case and see if that makes a difference. If it doesn't then I doubt it's because you're not getting enough airflow into the case.
Have you tried doing a repair for the OS?
Let me know if any of that helps
