Either get better media, like Verbatim, or use a different burning program.
ImgBurn is free to use, but if the drive doesn’t recognize the disks, you may not be any better off. Is this a new batch of blank Memorex dvds?
If you want to try ImgBurn, it is here: www.imgburn.com
The guides to burning dvd-video are here: http://forum.imgburn.com/index.php?showforum=4
If you do get the Memorex disks to work in ImgBurn, burn them at 8x if they are rated at 16x.