BUG: Missing UI

Problem
I can't play anymore for there is no User Interface in my game anymore.

Cause

• The User Interface can be turned of via F10 so that you can take pictures or make a video without the UI.
• Corrupt save, for example because you uninstalled an injector scripting mod the wrong way. An error occurs on load-up which makes it impossible to load the game properly. 
• Any ScriptErrors on loadup that prevent the game from loading properly.

Solutions

• Press F10 or ESC
• Try if reloading the game helps 
• Make sure to correctly uninstall Injector Scripting Mods. Refer to the mods on instructions on how to do that.
• Solution by Cyron43:
• Open the cheat console with ctl-shift-c
• Type resetsim *
• Hit Alt-F4 to be promted to save the game
• Restart the game, you should have your interface back
• If nothing helps, you will need a mod to correct that or load a backup  

Mods that help with the problem

• ErrorTrap can save most of these savegames.

Further Reading

• BUG: Invisible Sims 
• BUG: Frozen & Stuck Sims
• BUG: Missing Sims and empty UI when arriving in vacation town  
• Game Help:UI and Sim Issues
• General/Other - [Common] Missing Sims and/or User Interface 
• Lags & Invisible, Frozen & Stuck Sims