Computer is slow and sluggish?

Hi all, my computer is so slow and sluggish i have searched for viruses ,spyware,mail ware,done a disc clean up used cc leaner,done disc difragment as well i have 90% free space so any idear why its so slow dont know to much about pc so if you can help can you put it in simple english ,thanks
Update: Also i formated it twice
Update 2: and put a new fan in coz it was well dusty
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