Have you checked both the browser console and the live logs to see if a message is showing in either of those?
See also question https://forum.mendix.com/link/questions/105910
You made some serious mistakes. You can not revert back to a previous Mendix version without also restoring the data. That is why you always create a backup before doing an upgrade.
You propably corrupted your database now. IMHO to only way to solve this is by going back to the database before you upgraded.
Regards,
Ronald