Problem with Batman: Arkham City Harley Quinn’s Revenge and Freight Train on Riddler’s Revenge

For HQR, there’s a balloon right at the start, and when I pop it, the game freezes for three seconds, then takes me back to the start screen, where it shows the main game, new game plus, replay catwoman stories, etc. As for Freight Train, I click on it, loading screen shows, tells me my disc is dirty, and no matter how many times I clean it, it doesn’t work. Additionally, it shows invalid disc on the loading screen after I press it. I’m sure the problem is the disc itself, but I don’t know what to do about it. Any help is appreciated. Thanks.