I had a similar problem once.
In nero 6.x, look in the upper right hand of screen at drop down window. If it has "Image Recorder" selected then you will only make an image on the harddrive and be left with a (still) blank disc in the burner. Make sure to use the drop down box to select your burner.
I am assuming that there is power to the drive: you can eject and spin up the disc in the drive.
If you can't read in Windows Explorer an already burned disc or commercially pressed disc, one you know has data on it, then maybe the ribbon data cable became loosened at the drive or motherboard, or it is defective. Resecure the cable ends or replace with a known working cable.
If no solution is forthcoming, you may want to try the self test to see if you need to RMA the drive back to Plextor. See your manual or Plextor's website for instructions.