I had to start my game over and every time I try to log into the world, it shows up a blank screen! There are no scratches or prints on the CD, and I cleaned it as well. Any suggestions on what the problem might be?

There may be a scratch deep in the disk. The disk is covered my a thin plastic covering that protects the steel data of the game. If the plastic gets scratched it shouldn't be a big deal but if the steel is scratched it could prove fatal. Is the game owned because if it is then it may have been re-coated and deep scratch may be there? Either that or your console is old and the laser is weak. It's happened to me before.