Win2000 malfunction

[Gary]

One of our stand alone Windows 2000 computers without warning stopped loading CG Windows at the Intellicad shell and could only be exited through the task monitor. When repeated attempts failed even after reboots we uninstalled both Intellicad and CG Windows, then reinstalled first CG Win 5.00.10, then CG Win 5.50.03 when the former failed to load. Either version appeared to install properly with no errors, but neither could load past the Intellicad shell. We even switched Sentinel blocks with other machines and reloaded drivers to no avail. All other applications on this computer (AutoCad2000, Microsoft Apps, PhotoShop,...) were unaffected and remain operational. Any suggestions or fixes