I am having a really bothersome problem using the MSDOS prompt in Windows 3.1
to open a dos box.  When I am done with the dos box, I cant get back to windows.
If I do Alt enter to shrink the box or use 'exit' to close it, the screen goes
black and I have to control-alt-delete until I kill windows.  I get a couple
of screens about app not responding.

I think things are still alive under the black screen because if I alt-tab
to cycle through the running apps, I get flashes of text but then the
black returns.

This persists even if the machine is powered on and off.

I am working with an app developed using Borland's 3.1 application frameworks
and c++.  It seems to work fine.

Hardware is a 486 with 16meg ram; not on a network.  Video is a TSENG 
vga.  dos 5.0.

I reinstalled windows a couple of time but the problem comes back.  I am
using temporary swapping for virtual memory.

I would really REALLY appreciate any hints anyone might offer.

Thanks,