Computer lag/fps issues

[enfermera]

im having a problem with running wow, i used to be able to run wow perfectly fine, 30 fps in raids no problem. until recently when i struggle to even idle at 7-9 fps in twilight highlands, questing on low level alts or even pvp.
its gotten to the point where everything is on low, and im still running at 7-9 fps.

ive done a de frag on my drive every day for the past few.
all my movies/music/images are on externals that aren't on when playing wow.

any ideas what could be the cause?
will i have to re format everything or is it as simple as a corrupt wow file from a patch?

[vesseblah]

Check out temperatures of your computer while running games, sounds like overheat throttle. Also give more details of the hardware.

See stickies for more info on both.