You didn't note the age of the drives. While I've had some luck with updating the drive firmware it's no longer a viable shop repair option since a new drive is under 40 bucks and tech time would exceed that and to make matters worse the charge would be on the bill even if it didn't work out.
This is why you swap out the 1 or more year old drive and see if it's fixed rather than pump up the repair bill with time charges trying to save the drive.
I have DVD RW's on my two XP Professional systems and until recently I had no problem burning DVDs. About a month ago both stopped writing DVDs ? but they will write CDs. Both drives can not see a blank DVD RW, but they have no problem reading a burned or manufactured DVD.
I have used several different manufacturers DVDs in the past with no problem-but the plus DVDs did work better than the minus. Now DVDs from the same cone just don't work. One drive is a 4X 4 gig model (it lives on a P4 2.6Ghz with 1gig of ram) and the other one is an 8X duel density drive (its home is a P4 3.2Ghz with2 gig of ram). I am using Nero 6 to burn my DVDs and until recently had no problems.
Any ideas or suggestions?