I used to run CATIA V5R20 on the laptop running Window 7 and it works fine. When I upgrade my operating system to Window 8.1, CATIA does not work anymore. I try to run Compatibility Troubleshooter and change the Compatibility Mode to Window 7 but the application does not work too. Does anybody have any tips to get around this issue or I have to reinstall Window 7 back. Thanks for your inputs.