What is the model number of the external DVD drive you are using?
Does it recognize other DVDs?
If the DVD player is not functioning for any disc then you may need to reinstall your OS X.
Ok, so just with the Roland disc you are getting a grayed-out icon?
How are you accessing the disc? Through Finder?
Ok, then it sounds like the disc is faulty.. have you tried running it on a different computer?
You can try downloading the installer from the Roland website instead: