Trouble with nero vision express 3

I had to go back to my nero 6 to burn some video clips. First two times I burned clips no problem. Now though when I try to click my nero vision express 3 it will not acknowledge my external liteon dvd burner. It says I can create cd but that is it. This happen once before and I remember I was given tips on how to get my external dvd to be recognize but that has been so long ago I forgot how. Any one have any tips? Thnks!