Unknown error occured

So my mother recently bought me a Mac, to set it up she used her Apple ID. I needed to change to to mine so I signed it out through system preferences > Overview > Sign out.

Then I tried to sign in with my Apple ID, went through the steps and entered the verification code, nothing came up so I sent a new one. I typed it in and it kept loading for about half an hour and came up with “unknown error occurred” I notice a couple of my apps on the desktop had disappeared too, though their icons are still on the taskbar. (This is another problem).

I retried twice with the same results, Unknown error occured. On the 3rd time I noticed all my apps on the desktop screen were gone. (Still on the taskbar tho). I don’t seem to know whats wrong. Could it be just a unstable internet connection? Or am I entering the wrong verification code due to multiple resends? Or a problem with the Mac itself?