PC doesn't recognize DVD it just burned

[illus10n]

Can't figure this out. I use DVD Shrink to backup my movies and Drag'n Drop DVD to burn my movies. I was trying to make a copy of a copied movie and when I put in my copied movie in my computer (which just burned the movie) it does not recognize any disc in the drive. The Dvd's play fine in my 3 dvd players in the house. Some movies are recognized in my PC and some are not, this has happened with Sony, Memorex and Matrix dvd media. My computer is a Sony Vaio with a pioneer dvd burner/player it's about 2 or 3 yr old.
I took an original movie and burned a copy, however the computer did not recognize the copy then I burned another copy from the original and it recognized the 2nd copy. What's the deal with this?
Thanks in advance for any help.

[Zero G]

I have only had this happen twice with some no name discs. Out of a batch of 50, 2 did this. They both play fine in all my stand alone machines, but not my pc. I just chalked it up to the media itself.