In that case, we have to consider that DVD-RAM drive has a problem or that you need to be using DVD-RAM discs.
Do you have access to another computer that has a DVD-RRW drive and try that? It would eliminate the blank discs from the equation. Can a DVD RAM drive burn CDs and DVDs? - Yahoo! Answers DVD-RAM - Wikipedia, the free encyclopedia
From what I can make out, some computer manufacturers sell computers supplied with a DVD-RAM drive, but don't have DVD-RAM support meaning you'd need to update the drive's firmware.
It might be easier to bite the bullet and replace your DVD-RAM drive with a DVD rewriter drive.