Bit drastic,Mac.
Have you done the following?
Run all your antivirus / antispyware / antitrojan software? Plenty of excellent free programs here:
http://tinyurl.com/y83v23 (In particular A2 and AdAware)
Defregged your hard drive? Not as essential as it was, but still useful.
Sorted out your startup? You may have programs automatically starting that you don't need, Too many programs running at once can slow you down.
Removed unnecessary files such as temporary files?