Disappearing Start Menu

This is nearly the damnedest thing I’ve seen in a while. A PDC Windows NT 4.0 Server with SP6a and all the latest Security Rollups downloaded and installed. Standing still desktop. Click on Start and Programs. Immediately the Start Menu disappears. Click on Start again. Up pops the Start Menu list. Immediately the Start Menu disappears. You can’t click on a line item to pin it in place. Every time it disappears. Anyone have any thoughts for solving this problem? As always, I am much obliged.

Gary