The unit has been working fine for many years but all of a sudden, when I went to change the cd, the door popped open but won't close now. Whether there is a cd in it or not, the door will not close. No pieces have broken or have been damaged, as far as I know. If I put a cd in and hold the door down, it will play. But obviously I cannot hold the door down all the time. Please help! Memorex CD Graphics Karaoke System Model MKS2461