It sounds like your disk or reader is having problems. But to be sure, go to 'My Computer' and click on the DVD reader (with the disk inserted) and see if it gives you a list of files and folders.
There are instructions elsewhere on this site about getting MapSource on a new computer which I can't track down. It involves downloading and installing Garmin BaseCamp first
Garmin: BaseCamp Updates & Downloads then the latest MapSource
Garmin: MapSource Updates & Downloads. That will get you to a point that moving the map folder will be doable. Can you get that far?
Terry