Games that worked yesterday are now "Unreadable"?

Hey mate, it sounds like your disc drive is having issues. Can you please try these steps, to see if they resolve the issue? If they don't, you'll need to set up a repair for your console. You can do so (as well as check your warranty status) here.

Ok, I got all the way to the step that talked about removing the hard drive. I removed it, and it recognized NBA. I then tried playing a Quick Game and, again, it said "Disc Is Unreadable."

this is why i prefer to download my games from the game marketplace. no discs to scratch out

I am having the same problem, I went through all of the steps mentioned and none of them helped. My game is [Prototype] and the day I picked it up I had no problems at all. Beat the game repeatedly over and over and never had a problem for years. Started playing it today and got disc unreadable, tried installing. Same problem. I'm sure this isn't an 'odd' coinquencidence.

What's the condition of the underside of the disc?

EDIT: And try doing what the OP did and remove the hard drive. It's not a long term solution but it at least can point to where the problem is.

Not a single scratch, never ever do I treat any of my games intently or otherwise roughly so all my games are in perfect condition. It just happened to say unreadable and it's suggestion to clean the disc off is reduntent if the disc has no scratches or laser rings etched into it.

Edit: I just mentioned in the post above that I TRIED everything the OP did. Seems people are having trouble reading posts lately.

If you're going to be sarcastic no one's going to try and help. It's supposed to be users helping users not users running down other users who are trying to help.

Well I learned my warrant has been out of effect for 2 years. I reaaalllyyy dont have money to buy a new console. Also, where is Mister Fitzer? He has been the most helpful so far, no offense.

So it sounds like the game was working properly with the HDD removed, correct? Did the quick match then fail with the HDD removed, or was the HDD re-attached? If the game has no errors with the HDD removed, then we'll know the issue is with the HDD. Also, have you had a chance to try the disc on a different console, such as a friend's?

Well NBA 2K11 starts up, but is unreadable when you try to play a game. I had it removed and the game started, and it was still Unreadable when I tried to play a quick game. I was planning on trying to play it on my friend's xbox tomorrow.