Access Denied

recently have to change my main drive on my PC. Before doing that
I moved all media files and other important documents to a second
internal hard drive on the same machine. After setting everything up
(Win XP/SP2) I attempted to move all my media files and the
documents back but was not able to do so. I keep getting "access
denied, make sure the disk is not full or write protected and that
the file is not currently in use". When I attempt to 'open' a media
file using RealOne Player and MS Media Player respectively. A window
appear with the following message:
RealSystem Messages -
Requested file not found. The link you followed may be outdated or
inaccurate.

Windows Media Player -
0xC00D11D2: Cannot access the file
Windows Media Player cannot access the file. You may encounter this
error
message for one of the following reasons:

a.. This file is currently in use. Close the file, and then try
again.
b.. You do not have permission to access the server or other location
where the file is stored. Verify that you have the appropriate access
rights, and then try again.
c.. You do not have permission to access the proxy server. Verify
that you
have the appropriate access rights, and then try again.
d.. If you are trying to copy a track from a CD to your hard disk,
you may
not have permission to copy to the specified hard disk location.
Verify that
you have the appropriate access rights, and then try again. If the
problem
persists, try copying to another folder.

Some of these files are very important relating to my job.
have no idea what happened. Am willing to try any ideas. HELP!