Well, depending on how much data is on it, there is always the copy everything off, format and copy everything back...

The chkdsk thing should work, but it's strange that it is not letting you.

It's a stretch, but try this tool:

http://www.jrtwine.com/Products/DelFXPFiles/

Try this:

Close all open programs.
CTRL-ALT-DELETE and open task manager.
Close EXPLORER.EXE
Go to FILE and choose RUN.
Type CMD to open a command prompt
Then from the C:>_ change to the...

...still looking. You already tried a reboot.