Quite often the D: drive refers to the CD-ROM or DVD drive which is either empty ( no disc ) or full ( after all, ROM does stand for Read Only Memory ). Occasionally the D: drive refers to a separate partion on your hard drive, in which case use a programme like Partition Magic to reapportion or simply move some stuff from D: to C: ( or even to a CD-R if your CD-Rom is a writeable variety ).