Normally I will not post once another Member is working a thread but you are not grasping what Steven is saying. (Steven, my apologies for stepping in)
Your Xbox 360 & DVD Player cannot read blank discs, DVD-R, DVD+R, CD-R, etc, there must be data on the disc. Nor will a Wii, CD-ROM, DVD-ROM or CD/RW drive, home DVD player, so if they do not detect the disc, these devices are working properly.
In order for these Blank discs to be "detected" you must insert them in a DVD burner of the type that supports DVD-R discs. Currently on the market today, 99.9% of the DVD burners support both " - " & " + " formats.
Do you have a DVD burner? If so and the discs are not detected, then I am sure Steven can help but he will need more information, make, model of said drive, Operating System, burning software, etc....