Hi Roblevin, welcome to our forums!
Before answering your question, I want to tell you something about our forums. Our forums aren't just a place for getting a quick answer, they are a kind of knowledgebase as well. Because we greatly value this knowledgebase, we don't do any email replies, but only replies on the board. This gives the advantage that other people can profit from solved problems (etc) as well. Ofcourse, you can enable the email-function for a certain thread, so you'll be emailed when somebody replies to your thread.
That said, let me answer your question. You have a NEC1100a DVD writer you say. That means that this type of writer only supports DVD+R and DVR+RW media. There's nothing wrong when it doesn't recognize any DVD-R or DVD-RW media, as it doesn't support those discs.
The NEC1300a does support these kinds of discs. This is a so-called dual-format writer. Yours is single format and only can handle DVD+R and DVD+RW.