My MacBook Pro does the same thing, I had to buy an external DVDrom drive, even then it works when it wants to. I use to have a problem burning CD but DVDs were ok, but now it seems I can burn CDs but not DVD, on either Toast or Disc Utility. I suppose I am **** out of luck. I would try repairing permissions under Disk Utilities. If not then turn off the computer unplug cord and/or battery, hold down the power button for 10 seconds turn back on, when you turn it back on hold down the option the apple key and p, and r keys together it should restart it keep them down for 3 cycles and then give it a shot.
Rebug, " I can't go for that... No can do." (Hall & Oates)
Kmeaw, "Never gonna give you up, Never gonna let you down." (Rick Astley)
KuzMEAW CFW +Other Goodies = http://www.ps3iso.com/showthread.php?t=85528
Kuzco's Klassic Korner = http://www.ps3iso.com/showthread.php?t=87903