okay, when you're trying to playback a DVD the next time check taskmanager (press ALT+CTRL+DEL) if the CPU usuage is up to a 100% then there's something wrong in the communication between the drive and the m-board or driver curruption.
so you can do this;
open up the case
remove the cables from the drive and unplug them also from the board
attach them again (making sure they're firmly in place)
and reboot to see if the problem has changed
another option is, if you have to drives you can alwasy switch them around, adjusting the jumpers to suit