As said, try entering with your PS3 disconnected from the Internet. If it still doesn't work, try the "salvage files" feature found under "Options>Misc. Options>Additional options(not sure what the name is - just search through the options and find "salvage files")>Salavge Files".
If that still doesn't work, delete your GAME data (not save data). Export any replays and photos beforehand as it will delete them (you'll also have to redownload any stealths or promotional content). Reinstall and see if that fixes it.
If not, then it's most likely your disk.