both dvd drives play music/video but can't read files

I have two dvd drives (running under Windows XP Home) one ROM and one
RW. Both play cds and dvds just fine, but neither will read files.
Installation cds spin for a few moments, then go silent. The file
explorer can't find anything whn I click on it. (One dvd complains that
it's not ready, and the other one just ignors everything.) I've been
able to install new programs is via a dvd drive on a networked computer:
I can read the cds just fine across my home LAN. I upgraded the firmware
for both drives, but no change in behavior. I'm at a loss. Any ideas?

--Mark.