Why is my computer not recognizing my disc?

I bought Battlefield 3, and my computer is not recognizing the 2nd disk, it took about 30 minutes to an hour to recognize the first disc, and when i put the 2nd disc in, it hasn't come up in 1.5 hours! The PC just does not pickup the disc, it says it's empty.Why is my computer not recognizing my disc?
Take the disk out and clean it, but make sure you DO NOT clean it I a circular motion because that will only damage the disk. Get a damp cloth (lint free) and clean from the inside out (go with the flow of the rainbow streaks). Make sure to use a dry cloth to make it dry. Turn off your computer and wait a few minutes and turn it back on again. Try using the disk. If it does not work then maybe the disk was not manufactured properly but it could be anything. But make sure to not rely entirely because chances are that I am wrongWhy is my computer not recognizing my disc?
You could have scratched the disk or the disk drive may be damaged and can not correctly read disks , if it does not work on other disks consider replacing the disk drive with a knew one , they are quite cheap

Good Luck :)