First make space on your hard drive. Windows will not work correctly and will throw all sorts of errors and get file system corruption if your hard drive is too full. Get a USB external hard drive and copy all your data files to it - music, pictures, videos. Then delete the files from your internal hard drive. Next uninstall any unused/unneeded programs from Add/Remove Programs. Of course you should also make sure that the computer is virus/malware-free and do maintenance on it. Once you have put the drive back into shape by doing the foregoing, post back with the results.
http://www.elephantboycomputers.com/page2.html#Backing\_Up
http://www.elephantboycomputers.com/page2.html#Maintenance
http://www.elephantboycomputers.com/page2.html#Removing\_Malware
MS-MVP - Elephant Boy Computers - Don't Panic!