Windows 7: Desktop still having problems after cleaning interior after thermal ev

My computer used to shut down and a message used to be displayed that there was a thermal event. I opened the computer, remove the screws of the fan and cleaned the thing underneath it of dust which it had a lot( and of course other parts too). after that I put the fan back but I am not sure whether I put it in original upside down position or in wrong way, anyhow the wires connecting with the fan are now in between the fan and the thing which it cools but computer still sometimes shuts down suddenly even before booting. What should I do? should I re install the windows? thanks

In short you are saying that you removed the heatsink over the processor, cleaned it and put it back? If it's the case, you might want to NOT start the computer until you open it back and put some thermal paste between the processor and the heatsink, or else the computer will do as you say, shut down by itself because of overheating.

connected to the computer through wires. I just cleaned the heat sink beneath the fan by soft brush. thanks again