are you sure no other burn program has locked the drive? reboot the machine to clear anything using it. If it then wont work, run this fixit tool
Fix problems with CD or DVD drives that can
if that doesn't work then the burn lazer in the drive is probably dead
Lite-on drives don't last long: I've never had one last much over a year.
My experience is that Toshiba or Samsung branded ones are longest lived (both are made by the TSST joint venture) and LG ones are pretty good as well