Is it when you press the button on the drive itself? Have you tried ejecting it though software such as in my computer? Are any programs running that may be trying to access the drive? Does your drive have a little hole under the tray to do a manual eject?
I've seen this problem a few times before where it's actually caused by software, not power or hardware... Always try restarting when having any computer problems... If your drive seems to have power and should be in working order, I would suggest doing a clean boot in case some software program is hanging it up. You can find instructions on doing a clean boot here: http://support.microsoft.com/?id=310353