I don't have NXT 5 on my system now, but ideally if you have made a project and want to edit it later you will keep the project and all the source files intact and in the same place as they were when you made it.
Since nothing is ever ideal and you've deleted the old project and perhaps even its source files, try this:-
-put your DVD in your optical drive, and copy the Video_TS folder and its contents into a folder on your hard drive. (Ignore Audio_TS or Roxioplasma if you see them)
-Run Videowave, start a new project, and go to Add Photo/Video. Add VIDEO_TS.IFO from your VIDEO_TS folder to your new project, and that should import your video. Then you should be able to make your new edits and subsequently your new DVD.