dvd rom

My dvd rom works after I start my system. If I remove a disc, and insert it again, my drive is not accessible. I restart, and as long as my disc is in the drive I can use it. If not, I get drive not accessible when I put a disc in the drive. I checkthe sysedit and there is no information in the autoexec.bat. There is no text at all. What is the cause of this?