I had the same problem with 2 previous Plextor units.
CD burning/writing would not be affected but dvd burning/reading didn't work..power calibration errors...
Reinstalled Nero, Image burn, plextor stuff, you name it.
here's the fix for many units..
Shut down, Take the unit out but Don't do any "remove hardware"
or stuff like that since you will be putting it back in, turning the PC back on and Windows will be non the wiser...
cut the "do not remove tab" on the side of the burner.
this voids 1st year warranty unless you want to send it back but this is what they do to most of them..
Open the Plextor up. 4 little screws I think..
in the center of the inside you will see a tiny glass lense.
this is the laser/lazer?
take a small cotton swab and just dampen it in regular Alcohol.. DON'T SOAK IT..
Clean the lense in a circular motion,
don't worry if you don't see any dirt cause it's there in some form be it cig smoke, dust or whatever..
put the unit back together and turn it on.
I have saved 2 Plextors this way..
same errors like power calibration error, cannot read disk etc..and it is usually a not so clean lense...