Fresh install or upgrade?
Search - Disk Cleanup - c: - go through disk cleanup and more options. See what that gives you.
Also, you have 64GB of memory. If you have hibernation enabled you will have a 64GB hibernation file on your drive. To turn off hibernation:
http://support.microsoft.com/kb/920730. Page file can also be reduced/turned off: comptuer - properties - performance - settings - advanced - change - custom (fixed size: 1000MB) or no page file.