|"My CPU is overheating"|
Which CPU do you have? How about posting the temp reading?
"I noticed there is not much paste between the CPU and the heat sink"
How do you know that? If you took the heatsink off to have a look, you "ruined" the paste. That means the top of the CPU & bottom of the heatsink need to be thoroughly cleaned of all traces of the old paste, new paste applied, then the heatsink reinstalled. And the paste MUST be applied correctly. I can't tell you which method to use because you didn't bother to post your system specs, so find the instructions using the following link: