hello,
firstly, some specs of your pc would help so we can all see what hardware you are using.
when you put the processor back in, did clean off then reapply the thermal paste between the processor and the heatsink? The fast fan would indicate you are burning up your cpu, so I would not try to boot up again until you have solved the issue.
if you outline your exact steps in taking the processor out and putting it back in again, we can help.