I have one of these units that will not play DVDs. It WILL play audio CDs and VideoCDs fine, but on DVDs it just searches for a while the says "Invalid Disk".
take it to someone for repairs? get a new one? did you try a DVD cleaner disc? harsh language, hit it a couple times to show it who's boss, insult it, sell it, hook a ps2 up to it (if you can) and use that as your DVD player,