Wondering why you have so little room left, then download WinDirStat at windirstat.info. It is free, open-source, and easy to use.
WinDirStat represents each file on your drive as a colored rectangle. The size of the rectangle indicates the size of the file compared to the other files. Click on the big blocks of color to find files that are no longer needed and that may be taking up valuable space.
NOTE: Be sure you know what you are deleting before you remove something from your hard drive.