Windows not Showing

Hi,

1. I was using gitter.exe on a 64bit win7 computer for about 2 weeks.
2. At some point the windows would not show in expanded mode. Each instance shows in task bar with a thumbnail of image, but when I click nothing displays.
3. All is proper in the system tray
4. I've uninstalled/re-installed and checked the registry Any ideas on how to fix? TIA John