Run Windows Update to make sure your system is fully patched with all the latest critical updates.
Empty temporary internet files, the recycle bin, delete your e-mail deleted mail box items. run disk clean-up and defrag.
Do a virus scan of your system with the latest virus definitions.
Run Ad Aware or any other (free) spyware removal tool. Remember to get the latest update/definition files before running it.

Reboot, reboot, reboot ..... HTH