open My Computer, right click on the cdrom drive that isnt autorunning.
select the second tab (Auto Play)
make sure it is set to "prompt me each time to choose an action"
it is possible it is set to one of the other three settings hence why it opens an explorer window.
run Help on your computer do a search for "cd autorun"
choose no 11 in the microsoft knowledge base section. there it tells you how to check the registry for the missing commands.