|A couple of thoughts come to mind.|
First: You mention DVD-R, but are you aware that this is a specific type of DVD media? That is to say, DVD-R discs and DVD+R discs are different so you have to make sure that your drive can read or write that particular type of disc.
Most newer systems can handle both, older systems may only support one, but there are no guarantees, the only way to be sure is to check your system specs.
Second: Many older systems don't support dual-layer discs. Many of the commercially recorded movies come on dual-layer DVDs these days.
So, the first step is to determine what type of DVD you have and whether or not your DVD drive supports it. If they're compatable, then you'll want to dig deeper.