Viewport navigation slow during smooth mode in 3ds max

[chow choppe]

Hi everyone

 

I am facing a problem with my viewport navigation in 3dsmax

When i try to orbit or pan a scene in 3dsmax Smooth mode the navigation gets really slow. Even if i try to isolate 2 objects and try to orbit the navigation gets really slow.

But if i orbit the same scene in wireframe mode the navigation speed is fine

I am using HD 4870 card

 

It was working fine few days back

 

Whats the problem?

 

Thanks