PC-DVD not detected

I am trying to install Unreal Tournament 3 and Crysis Games on my HP Pavillion dv6000 Notebook running Vista Home 32 bit. Unfortunately the Games discs in both cases are not detected. I am able to see an autorun and manual run for another game disc (Orange Box). But the problem seems to be selective. The DVD-RW drive of the PC seems to detect some CD's and DVD's and completely disregards other DVD's (neither autorun nor manual double click) which USED TO run fine earlier. Do i have a problem with my DVD drive, if so how come some other discs run fine. Can anybody help, because am sure the game discs are fine.