I'm not sure you're actually booting from that dvd. Try another way- reboot with the dvd in the tray and tap F12 repeatedly till you see a menu where you can select the boot device, choose the dvd drive, hit Enter.
If its still no joy, you may have a bad burn or a bad iso. Try reburning the iso at the slowest possible speed, also try using a new disk of good quality.
What is the origin of the iso, may be a defective one.
Finally, did this computer come with windows 7 preinstalled? If yes, then other options are available.