no video in itunes (only audio with a black screen)

I've tried the tips here :http://support.apple.com/kb/TS1718

And the one that works is under the section :

Disable Direct3D video acceleration in QuickTime for Windows Vista or Windows 7-

Deselect Enable Direct3D video acceleration in the Video section

Click "OK"

But it only works for 1 video. When the next one starts, check box is checked again. If I uncheck the selection, click Apply and exit then go right back into Quicktime, the box is reselected.

The same with the next solution.

Anyone know how I can make the change permanent?

Thanks