Try to clean the read laser and the laser pickup, by using a DVD cleaning disk. If this does not work you may have a misaligned laser or pickup.
That may sound like a canned response and it is, however it is a good start. I would also check the format of the video on the DVD-RW, and make sure the DVD player is set to display that format. Also might I suggest that you try the documented Disk loading instructions. I know that sounds stupid, but I was working on a customers DVD player one day and I downloaded the manual, and I was shocked to find out that I was not following the recommended loading procedure, once I did that all of the disks worked (stupid? yes, but that's how things are now).
As I said try to clean the pick-up and laser, check the format of the DVDs, and then follow the recommended loading instructions.
I hope this helps