CD DVD drive problem

Hi,
I'm running Win 2k SP4
I have CDR & a DVDR drive in my PC if I insert a data or audio disk in
either drive, the drive spins up but nothing else happens, when I check in My
Computer both drives show as CD Rom & selectng either one brings up an error
message about being unaccessible.
If I try to burn to a blank disk, that works OK (using Nero 8)


If I boot the PC while there is a disk in either drive, then they are both
accessible.

Any suggestions?

Thank you