[Pete Cave]

It’s been a while since you posted this, but for all guys like me who are still facin’ this weird problem,
here’s one possible solution.
Seems like this weird behaviour of the zoom/ camera-movement funktionality
as well as black viewports can be caused by some graphic driver updates.
In my case, those bugs appeared as I updated to the newest ATI-drivers.
Maybe a simple roll back of your drivers, like described might solve it.

https://www.ehow.com/how_8198854_roll-graphics-driver-windows-7.html