Is your PS2 Mod-Chiped?
Mine is, and ever since I got it chipped, it wont play DVDs anymore... Stupid thing
And, before you start spouting all the "But, moding is illegal!" carp, in Australia here, it's not. The high court ruled it to be 100% legal
The reason I have it chipped is that when my mum was in the UK, she bought me a whole load of games as pressies, little did she know they all had region encoding on them, so I went to Sydney, forked out $30, got it chiped, and they all play now
But, DVDs don't play at all.
Some original DL one's do - Burnt ones don't, but havn't tried with burnt DL's yet.
And again, before you say "Copying DVD's is illegal", I know it is, I'm talking about the skate/funny stuff DVDs that my mate makes - they're quite fun
Hurray.