Hi pegee,

What OS are you using?

Have you tried setting the external monitor as 'Main' instead of running it as a secondary display. If doing that causes the 3D view to work properly, then I'm guessing the graphics chip in your notebook isn't able to handle two OpenGL 3D display overlays.

If using XP, one other thing to check, make sure graphics acceleration is set to full.

Lastly, have you tried running Sweet Home using the DirecX fix, see if that works as a secondary display? Have a read here.

db4tech