I've got a Toshiba l-500 that's about four years old now, and is otherwise working fine, but it doesn't seem to want to recognise any dvd I put in. It's loaded dvds for games in the past perfectly fine, but now it doesn't seem to recognise that the disc is there. Help please?

THe DVD drive may have failed... it is 4 years old.

Have you tried a CD? If not try any type of CD, music or data, if it won't recognize a CD either then the drive is probably / definitely gone.
Although, just because the CD works doesn't mean the DVD will, it could still be malfunctioning as a DVD player.

Have you recently uninstalled any CD/DVD burning programs? If so there is a "upperlimits" registry bug that may be affecting you: Your CD drive or DVD drive is missing or is not recognized by Windows or other programs (http://support.microsoft.com/kb/314060)