Slim chances to make it work again, but if you have minor scratches, you can try rubbing it off with a pencil eraser and than a clean fiber cloth. If you scratches are deeper, try a polish solution and clean cloth. Also if you have an old DVD player around something that reads DVD's at lower speed, it may be able to do the job. BTW, there are more solutions if you type fixing a scratch DVD on youtube.
Either your disc has gone bad and unfortunately will have to get another copy, I always make backup copies of my DVD's.
Or you could have some crud on your lasers lens. Do you have a DVD cleaner, have you ever cleaned the lens on a DVD player?
If you player plays other disks fine, then its your disk that's bad, if the machine won't play other disks, then clean the lens or you have to find a new machine cause repairs will cost you more than buying a new one.
There are disc cleaners you can buy, or you can try to polsih the disc and remove a thin layer from the top, hopefully buffing out the scratches. This is a last resort though. Your disc may just be too scratched...