might be the dvd software your using for playing dvd's might try a different one.
does it only do it with the discs you burn? after you reboot to get out of the lockup and try it again does it lock up a second time.
used to have some dvd software that would play a movie fine but after closing the movie it wouldn't release those resources back to the system and so the system would become inoperative. switched software and it stopped.