Have you tried Disk Cleanup?
If not , try that and see if it helps... keep in mind it may take several hours for it to complete depending on the size of your harddrive.
Make sure all applications are closed and dont work or use your computer during clean up.
1. Goto "My Computer" from your Desktop
2. Right Click your Hard Drive ie. (Local Disk C
3. A menu will come up and then click properties
4. Click the Disk Cleanup button on the bottom right
5. After its completed, reboot and see if that helped