It doesn't open by physically using the button? Or via software?
Does it open/release when you insert something (like a paperclip) in the hole to trip the eject mechanism?
If so, inset a disk & close it up - is the disk recognized?
If a disk is recognized, you may simply have a problem with the button/mechanism.
If it's not recognized, you may have a connection problem with the drive.....or a drive that has failed.