Re: My sims can't go up the stairs?
If you have mods/cc in your game, remove all of them to see if the game works better.
For example, move the mods folder from C:\Users\Username\Documents\Electronic Arts\The Sims 4 to your Desktop and start the game.
If not, try building two floors with just a pair of stairs in them to rule out that something is in the way.
