I'd recommend doing a Disk Cleanup
and installing and running CCleaner (don't run the registry cleaner, and carefully look through its settings to make sure it doesn't mess anything up more). Also go into Run and type msconfig, go to startup tab, disable anything you know you don't need....my advice, if you don't know what it is, don't disable it
Is your system fully updated? What antivirus are you using? How much RAM does your system have? I see you're using 64-bit OS, IMHO you should have more than 2GB to get the best performance.
What also might be a good article to look at is the Optimize Windows 7