Memorex dvd burner won't read discs

I have a Memorex external dvd burner (16x double layer ieee-1394a purchased May 2007) connected to a dell desktop (xp) via usb. For the past 3 months it has had problems reading blank and burned discs. I reinstalled windows several weeks ago but the problems have persisted.
When I insert a blank dvd (Verbatim dvd+r) it usually clicks and spins until I press the manual eject button. During that time I can’t access or progress in my dvd burning programs (Nero or Roxio). Right clicking on the drive icon in my computer does nothing. As soon as I eject the dvd the program opens and I can right click on the drive icon again. Before this problem started (and occasionally now) it would just spin for a few seconds and then recognize the dvd. On the few occasions it does recognize a dvd now it burns it correctly.
It usually recognizes burned dvds as blank dvds and occasionally won’t stop spinning until I press the eject button. The problem isn’t with the dvds since it will sometimes read that same dvd properly at a later date (even when I don’t clean the dvd between attempts).
Thanks.

Try opening the drive and cleaning the lens.