I suppose this is a classic case of what's wrong - the DVD or the PS2 - especially if you bought a new PS2 "recently". The acid test is to take a new condition DVD and see what happens. If it loads as you'd wish, wash the others in warm soapy water and try again. If the new DVD doesn't perform as you'd wish, take the PS2 back to the #####r under warranty.

Have you had the PS2 modchipped recently? A calibration may have been performed then contributing to your problem. But I favour my first answer.