I am using a windows computer and if you are playing Dolphin and then switch users, when you come back, Dolphin is frozen on a black screen!
Any help? Specs in signature.
...don't switch users without saving?
That's scarcely enough info to tell you what's wrong. Are you using different Dolphin folders for each user? Which users are they, e.g. is one a guest account, or an admin? What are the settings for Dolphin for each user? When switching, does Dolphin still play fine on the other user? One of theses users might be the culprit rather than just switching users in general. What happens if you log off as the user instead of switching? "Switching" and "Logging off" users are technically different actions in Windows; logging off may be what you need to do.
At any rate, Axxer's advice is the simplest and most direct solution. If it's not necessary to switch users, don't.
I'm switching from admin to admin, and I'm playing Dolphin on one and Dolphin is not running on the other, and I think there are different user folders.
Did you pause emulation before you switched?
When you switch users doesnt the OS put the former user in a hibernation state? meaning the video backends are shut down entirely so he would always get a black screen.
That's why I suggested he look into logging off one user then logging in as the other instead of switching users, to avoid any problems like that. At any rate, logging off should only take a few more seconds than switching.