We're asking what software you're using to attempt to play the DVDs. For example; "Nero Showtime". "Power DVD", WinDVD, or the Windows Media player itself. The Windows Media player WON'T play DVD without a DVD "Plug-in".
If you have software installed that is designed to play DVDs, then your problem could be hardware insufficiency. IE processor to slow, etc. The things that mailpup was pointing out earlier.
Please reread our earlier posts, then post back with any other questions, it's not a problem, really.