It sounds like you were copying from your thumbdrive to your C: drive, and that windows still has something "using" the C: drive.
Try reading this HERE, and deleting the page file, it's the only thing that I can think of off the top of my head that will keep the C: drive in use.
I've had a similar error, but with a thumbdrive (not a hard drive), and have had to end all my programs in MSCONFIG in the start up menu to release the thumbdrive (I then went back in and re-enabled everything I had unchecked).
Also, boot into safe mode (should be done by restarting your computer, then tapping either F8, F10 or F12, but they vary depending on the manufacturer) and do a defrag and then restart.
If none of this works, please post back and let us know (well, let us know either way!
), and we'll continue to help you!
EDIT: You can also check out this link HERE
. It's a nice little tutorial that I've done before to help clean out the temp files. I don't think it mentions cleaning out the temp files in Internet Explorer (or your web browser), which you should also clean out just for good measure!
Edited by stevealmighty, 22 November 2006 - 02:56 PM.