Here are a few ways i know on how to fix a disk that has been scratched or had been in an xbox that has moved.

1. Minor scratches - Toothpaste, i know this is silly but it really works.

2. Get a friend to let them borrow there disk and install it onto your hard drive.

3. Get some Cloth, such as one you would clean glasses with, and wet it. In a pinch, you can use a wet piece of toilet paper.

4.Use your wet piece of cloth or toilet paper to clean the shiny side of the disk (Not the side with the name and picture).

5. Put it in your XBox, and it should work. If not, try cleaning it again, to a maximum of 5 times.

6. if nothing works you can allways take it to your local Blockbuster / game station ect.
Will only cost 2 - $2 and if your lucky like me i got it done for free because they had lost the barcode