Make sure you are logged out of SimCity and Origin
Delete your SimCityUserData folder - default location is C:\Program Files (x86)\Origin Games\SimCity\SimCityUserData (don't worry, the game will recreate it when you log in)
Set Origin.exe and SimCity.exe to "Run As Administrator" - right-click the file, choose Compatibility tab, check the box "Run this program as an Administrator"
Log in to Origin; make sure it's updated to the latest version
Start SimCity and try to load your city again
Hope this helps. Good luck!