Is it cpu problems?

To add more info, it went out 2 weeks ago without warning. I ususally do heavy gaming on it. Ex. 8+ hours a day on weekends . It has 750± MB of ram.

when you replace the cpu always put new paste after removing the old one

I didn't replace tho CPU, I removed the heatsink and put it back on.

When you remove the heatsink you ALWAYS need to replace the thermal paste. It goes between the CPU and the heatsink.

So does that explain why my computer freezes when the fan gets hot?
Where do I get thermal paste? If its only available online, I can't get it. Do they sell it in best buy? Sorry if my grammer is off, I did this from my phone. Lastly, will anything else work like toothpaste or any other gel?

That doesn't help. My grandmother is still very alive thank you.

Very possible, yes. But when it comes to thermal paste, No substitution. You must use a thermal paste designed for the application. Go to Radio Shack. They sell Arctic Silver 5. And probably others. See if they have Arcticlean cleaner as well. (if not, use acetone found at Walmart in the paint section)
Carefully remove the Heat sync fan (HSF) and the CPU. Always hold the CPU by the edges, never touch the pins side. Don't bend the pins. Clean the flat heat spreader (top) of the CPU with the cleaner, as well as the HSF's contact surface. Then put the CPU back in its socket, place a tiny grain of rice sized dab in the center of the CPU's heat spreader and assemble the HSF to it.
http://www.arcticsilver.com/instructions.htm