GTA 4 Problems

Hi there i purchased gta4 for my xbox when playing it first time it loaded and i started to plar the game then i decided to lye my xbox from verticle to horrizontal. The disk got a massive scratch all the way around the disk. i turned the console off straight away and took out the disk i then went and purchased another copy of gta4 but it loaded up then said clean dist error from the right, i took it to the shop got a replacement and that too said the same error message. but it cant be the disk as they are brand new any other ideas after the scratch it wont load past the start credits. first time i actually got to play. Please help


Greg