The problem is likely software.
I have to regularly reinstall M$ office to keep it running properly.
If that does not solve it, I'd do an 'archive and reinstall' of mac os x -- sounds hard, but it's VERY easy and reliable. The mac will save all your prefs, move the old system to a 'previous system' folder, then add an entire fresh OS. Then run software update to make sure all is uptodate, repair permissions in disk utility, and you'll have a brand new laptop.
If reinstalling the software does not fix your problem, run the Apple hardware check CD that came with your machine.