I have such a machine and had this happen. I had forgotten to FINALIZE the DVD when it was in the Sony. Back to the Sony, finalize it and then it worked.
May you be so lucky if it's the same thing.
Okay, so I bought a 27" IMAC essentially as an expensive toy so I can keep pics, videos of my twin daughters. I have some old VHS tapes that I have converted to DVDs using the dubbing feature on a Sony VHS/DVD combo. When I put the DVD in the IMAC, it tells me I've inserted a blank DVD. When I open Finder to look at it, I basically "untitled DVD" and IMAC asks if I want to burn it. I want to put the video on the IMAC so I can edit it. Can anyone offer any advice?