Slow Slow Slow!!!!!!!

Ok so up until my a few days ago my computer has been fine... but all of a sudden it just became slow all the time . I'm winning windows xp pro. I have 3 hardrives : 2 are 90 gigs each and the other is 40 and only one of them is nearly filled up, I have around 780 mb of ram i've done virus searches and it didnt find any viruses ive also done a registry scan (whatever that is and cleared that up) this is really annoying me as a play games on my computer alot and theyre really slow now, i also have a 128 mb gforce 4 video card. PLEASE HELP!

Any new hardware & or software? Any changes you made?

You could try a System Restore.

You could try check disk:
start > run > cmd
in the new window type chkdsk/f
when prompted to run on boot choose Y & reboot
this will check for & fix any disk errors.

Also perhaps post a HijackThis log in the HijackThis section:

Please follow the instructions HERE 1st & HERE 2nd & then post your log in a new thread in the Spyware, Adware, Viruses and HijackThis Logs section.
(Not in this section please).

You could unistall any programs you arent using, run a disk cleanup and also defragment your HD if you havent in a while. This may help speed up things.