You could try to roll back to a previous saved system and just eliminate whatever software installation has caused the problem.
I had a similar problem with my wifes duo-centrino 1.6ghz laptop running XP. So slow as to be almost unusable.
Tried to adjust this and that for a few hours and eventually just did a reinstall from scratch. Was OK after that. In hindsight it might have been better to roll back to a previous saved system first, but there were other reasons for a reinstall that made sense at the time.
