1 Save all programms and photos and videos to an external hard drive all safe no virus
2 Full destructive recovery, will reset to factory setting ie like brand new again
this can be done by the recovery dvd burned by yourself or find the menu on start up, the option to do this usually F2, F8,F12 one of those just google it or do search on your computer "recovery" there will be something
I have done this all the time for people with same problems , slow , programmes not running, full but no saved data
the cleaners and virus checkers, defrag, disk cleaner all do ok but only temporary fixes
Just wipe the computer and start again runs like new may take a while but defo worth it any probs just pm me and i can talk you throught it