Macbook Air stuck login - help!

I was trying to shut down some processes because my MacBook was using to much battery in short time. I accidentally shut down a wrong process which made my desktop disappear and even though it said safari wasn't open all I could see was safari. My keyboard seemed to be disabled too. So it managed to get to the log in menu, but accidentally switch to the guest account that my computer is now stuck on. I have a defect power button, so I can't restart it that way. I have tried to drain the battery and let it run to 0% but it just starts up with the same login screen as before there is like a spinning wheel under the "guest account" text and I can move the cursor, the keyboard seems to work but nothing happens. I let it think all night and that didn't help either.
Anybody who might have tried something similar or knows a way to shut down/restart the MacBook without the powerbutton?

Annastruwe said:

Anybody who might have tried something similar or knows a way to shut down/restart the MacBook without the powerbutton?

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Well typically you click the Apple menu in the top-left corner of your screen and shut down/restart from there. You could do it from Terminal. You'll likely have to authorize as an admin user to do it though.

Shutdown your Mac using a terminal command — finiteloops.com