This is such a frustrating error. Some basic things - If you installed any mods, delete them. Reboot your machine to make sure there are no processes running in the background.
Here are some things to try, I hope one of them works:
1. Go into the city that is loading, then go to region view and see if you can load the problem city from there.
2. Make sure your firewall and antivirus are not blocking SimCity.exe, and that it is added to the exception lists. If you have BitDefender installed, disable it.
3. Run SimCity as administrator
4. In Origin, right-click SimCity icon, Game Properties, check the box that says "Disable Origin In-game"
5. In Origin, right-click SimCity icon, choose "Repair Game"
6. Run SimCityRecovery.exe Default location is \Program Files (x86)\Origin Games\SimCity\SimCityRecovery
7. Delete everything in the SimCityUserData folder and load the game again. (Program Files (x86)\Origin Games\SimCity\SimCityUserData)
If none of the above works, you could try calling support to see if they can roll back your city. Otherwise, you may have an unrecoverable city. Good luck!