Strange but true…………….. When you write a DVD using Pinnacle Studio, you are almost certain to find that it will play correctly in a hardware DVD player. However, you may well find that you cannot play it in Windows Media Player. What you need is Media Player Classic (for Windows). It is a cost free piece of software with no padding, themes etc. It does however player CDs and DVD very well!!! You can find it here;
http://www.free-codecs.com/Media_Player_Classic_download.htm

There is a good entry about it in Wikipedia.; http://en.wikipedia.org/wiki/Media_player_classic

Basically; Put your DVD in the drive. Load up MPC by double-clicking. From the Menu Bar Choose; File-> Open DVD. Or press the combination of keys; Ctrls+D. It works well!