I'm assuming that your d: drive is a hard drive. If it's a CD or zip drive, you may be having problems with a bad disc, bad hardware, or bad connections.
If it is a hard drive:
In Windows NT/2000/XP using the NTFS filesystem, files and directories have security permissions, which can exclude access to certain users or groups.
A network "shared drive" can also have permissions set to exclude certain users or groups.
You'll need to ask someone with the proper permissions (administrator?) to change the permissions to allow access to the files, directories or shared drives.