Your system was working fine then it suddenly wasn't working so fine. Surely it must occur to you that possibly you MADE a change to the software on the system.. I believe you mentioned you changed operating system.. then logic dictates that the software change is the most likely culprit of this problem.
You start from the bottom.
Heres an example. If you change your graphics drivers, and then your system slows down do you think you should -
a) check the graphics drivers for issues and possibly roll back the drivers
b) buy a new CPU and PSU and overclock your whole machine without having any knowledge of overclocking.
To the guy obsessed with overclocking - please keep your obsession to yourself, it is not the solution to every problem, I have had to deal with so many destroyed mb's, cpu's, entire PC's because of bad advice to inexperienced users.