|"The old one was accidentally damaged when cleaning the fan. The pins got bent"|
Let me guess - you attempted to remove the heatsink & ripped the CPU out of the socket in the process? Next time (if there is a next time), run the system for a bit to heat up the CPU & soften the thermal paste, them shutdown, unplug the power cord & remove the heatsink. With the paste being warm/soft, the heatsink should come off with very little effort. You should NEVER have to yank or pull, just a gentle twist to break the bond is usually all that's necessary. And as Fingers said, if the pins were just bent but not broken off, all you needed to do was straighten them.
"nor did I apply new paste. I am assuming now that these errors probably caused overheating??"
You MUST apply paste & it MUST be done correctly. You can buy "Heat Sink Grease" at Radio Shack for about $3.
Here's the application instructions: