Did you make the DVD? As there are no Lion DVDs other then if you made it. Apple never supplied Lion on DVD.
Use the Mac you originally created it on to make another.
Use the Recovery HD partition to reinstall Lion. Command+r at startup.
Use the Online Internet Recovery system to reinstall Lion. Command+Option/Alt+r at startup and hold those keys down until you see a Spinning Globe in the center of the screen.
If you wantr to make another DVD or USB thumb drive of the Lion install files use Lion Disk Maker, a small program, that does all the extracting and burnin to DVD or USB thumb, your choice which one or both if you run it twice.
But you first need to download the Lion installer and save a copy of it. There are several ways to do that. Look at this TIP.