Harold,

Yes. No.

There isn't an on-off switch for the 3D view, but there is 3D view --> Display in a separate window. (also accessible through a right-click in the 3d preview window)

Maybe you accidentally activated this option?

If not, you have to provide more information about your problem. Did you change the configuration of your computer? Like every program, SH3D has its bugs, but most 3D problems tend towards what is described in the FAQ .

Hans