DVD drive only sees CDs

I have 2 Plextor DVD recording drives (740 & new 800). I have them installed on a home machine with XP home and an office machine w/XP Pro. I had successfully ripped DVD's for the past 4 or so years. About 2 months ago my 740 started switching from a "DVD drive" to a "CD drive" in "my computer" when I inserted a blank DVD. I have tried 3 different brands of DVDs and took the old 740 to work and got the same result with both drives on both machines. I am unable to rip DVDs as Nero waits for a "DVD" to be inseted. I have tried other ripping programs also. This certainly seems to be the result of a change in XP.

Help please.