MY SYSTEM NOT INSTALLING WINDOW VISTA

Hello,
MY COMPUTER IS NOT ABLE TO READ INSTALLATION DISC OF WINDOW VISTA WHICH IT EARLIER USED TO READ. I had installed window xp service pack 2 in drive c and vista in drive d . it worked for 2years without any trouble. Of late I had to format C to install xp again. Then I tried to install vista in D after formating it like before but the system says that the disc is empty. I tried it on other system and it installs smoothly. I tried other dvds in my drive and it works fine. I HVE SPENT SEVERAL RESTLESS HOURS OVER IT. ANY HELP WOULD BE IMMENSELY APPRECIATED. THANKS