Keeping your computer up to date on the latest security patches available from microsoft can not only protect you from getting infected, but can also stop you from getting infected again after a virus or spyware cleanup.
Visit http://windowsupdate.microsoft.com/. This will run a scan of your computer, and let you pick from the latest updates your computer needs. Install these, restart your computer, and then run windows update again. Do this until it says there are no more Critical Updates available.
Once you get your computer up to date, you can set your computer to automatically download and install these security fixes for you in the future.
