David -

I've experienced similar issues with other programs (not ETABS). The solution for those programs was to completely uninstall the program, delete the directory it had been installed into, then then re-install it into a totally different directory. In the case of the other program, the issue was caused by one of the following:
a) a corrupted file in the program directory that was loaded when the program started and caused the program to be unstable. Hence the deleting of the original install directory.
b) a bad Registry setting. Hence the uninstall of the program, which should remove the offending registry entries.

No promises that this will work. But, I thought I'd share in case it helps.