LG Super Multi will not detect DVDs in the drive

First off the model I have is not the one listed above. The picture is the closest I could come by. I have a LG Super Multi DVD Rewriter model #GSA-E40L. The back of the machine say's it was manufactured in March of 2007. The problem I am having is the machine will not reconize any dvds that I put in. When I enter "my computer" the icon for the drive says it is a CD-Rom drive. If I push the open tray button on the machine and the tray comes out the icon changes to say DVD-RAM drive. Insert a dvd movie or a blank dvd close the tray and the icon goes back to the CD-Rom. If I try to run the dvd by clicking on the drive I get a message E:\is not accessable incorrect function. The funny thing is that when I first got the machine a few months ago the only type of media i used was in dvd format. All went well until i used a regular cd rom. It played the cd rom fine but when I went back to use a dvd it did not work. I still can play regular cds no problem but nothing happens on movies or blank dvds. On very rare occasions the name of the movie will come up under the drive but it only opens folders with the audio and vts files. I can then click on the file and tell it to open with the program I choose. The machine that I am using is a external drive connected to the computer with a USB plug. I am running Windows XP on a fairly new Toshiba Satelite notebook. When I first installed the unit windows detected it and said that it was ready to use. It came with a cd and I installed the following programs: PowerDVD,Power Producer and Nero Express with LightScribe Support(the writter does Lightscribe)I have seen other post where people have had the same problem that I am having but have been unable to find a solution. Sounds like the drive switched to cd rom and will not switch back to dvd. (I know this sounds very simplistic and my not even be relavent to my problem) I have not added any programs other than the ones mentioned above or deleted any programs since the machine was hooked up. Any help with this problem is very welcome. Thanks for your time. Marcus