iDVD 7.1.2 starts with a blank screen

Try this basic troubleshooting fix:

1 - delete the IDVD preference file, com.apple.iDVD.plist, that resides in your

User/Home/Library/ Preferences folder.

2 - delete IDVD'S cache file, Cache.db, that is located in your

User/Home/Library/Caches/com.apple.iDVD folder.

3 - launch IDVD and try again.

NOTE: In Lion and Mountain Lion the Home/Library folder is now invisible. To make it permanently visible enter the following in the Terminal application window: chflags nohidden ~/Library and hit the Enter button - 10.7: Un-hide the User Library folder.

OT

There are times that there's a hiccup of sorts while the application is writing to the preference file or cache file.