FPS Problem

Well i know it isn't the first thread about fps problems, but i am in a special situation, few days ago my pc started to work really bad and i dont know why,
I tried unninstalling antivirus, finishing unnecesary programs and analysing my pc with antispyware and antivirus and nothing changed,

About this problem,
If you can see the picture http://img40.imageshack.us/img40/940/checke.gif, you can see (left) my fps in one of my last demos, kz_kzlt_femtbhop, and that other one (right and current) you can see how my fps down in a frame, I can't found a correct solution, i am asking here because maybe some person had same problem and know a solution, just this, i cant record a shit, i fell my pc so lag

just that, if somebody know a possible solution It will be welcome

reinstall or format c?

You sure your computer aint getting too hot? That's mainly why my pc gets low fps..