Drive letters do not show up in disk manager but do in windows exp

We failed to plug in the external hard drive for a scheduled incremental
backup using Norton Ghost. This created a phantom partition with a drive
letter G:. Following Symantec's instructions, I went to disk manager and
deleted the partition. Since doing so, the drive letters for my operating
system (C and data disks (D do not show up in disk manager but do show up
correctly in windows explorer when I open "My Computer". Since this
happened, I have not been able to schedule automatic backups because Symantec
shows the drives are hidden. This is my wife's computer she uses in her CPA
practice and there is a lot of specialty software installed. Reinstalling
Windows would wipe out too much and the preinstalled OS that came with the
computer will not allow a repair install. Any Ideas?