CPU issues (I guess overheating)

Jul 4, 2014
5
0
4,510
So just change the case of my PC that wroked pretty fine and usable for what I was doing on it. The new case that isn't full of dust and it's far better than the other one (on that other case I had to play wihtout a side attached so the pc won't be so hot, it was like an oven). Now things wrok worst, from what i notticed in the task manager, my CPU is very instable now, low-high readings for almost everything i do, if I try to play LOL, the game that wokred like ~50 FPS (playable for me) now works to 10-20 FPS. So my guess would be the termopaste from the CPU and cooler since i tear my PC apart now isn't working good anymore, but since I don't know for sure I have to ask you guys.
PS: I have a better CPU that I didn't used in over an year, attached it to my PC but the PC wouldn't start (just a second then it would turn OFF), again guessing the termopaste was worst than this one that allows my CPU to overheat and if my PC would start with that better CPU it would ruin it.
So the question, could this be the problem to my PC?