I used to play T
ony Hawks: Underground on PS2, but then the game must of been scratched (this was back when I was completely careless towards these games) and I tried to save it, but it just froze; for about half a day..
So, I decided I had to restart the Playstation. As the game loaded, it froze again, but this time, I didn't touch or do anything. It had recognised my memory card in the console and just would not operate, because forcing a dangerous restart like that must of given it an error.
But then I decided to explore the memory card, and delete all Tony Hawks game saves. I got back into the game, and it worked fine.
Maybe something fixable like that happened with your memory card?