I've had to crack my PS2 open a couple times when it hasn't worked, but I've never encountered the problem you're talking about. I had a problem where it would make a clicking noise when it would spin and no game would run. I opened it up and found - I shit you not - earwax and a piece of toenail inside the machine's gears. Got that shit cleaned up and BAM good as new.
I guess my advice is to crack it open, check everything out and see if anything unusual appears in the machine.