What version of Nero are you using?
WHat program did you use to rip the DVD to your harddisk (although this doesn't appear to be relevant as it is Nero who doesn't recognize the disc)?
What drive do you have?
What operating system do you have?
What brand of media are you using?
Did you select the correct drive in Nero?
As you can see, a bit more information would be helpful, as well as a more descriptive title than "Help!!!!" (but that has been edited now). The more information you provide, the easier it is for people to help you....