Chosen Solution
I changed the name of my laptop and I got “You must restart you computer” so I restarted it, when the laptop started it required iCloud login and many logins. After logging in with same password, the window started as a new Laptop. no photos, no music, no files. So I checked the storage from “About This Mac” > “Storage” and found that there’s no data has erased and the storage is still the same as before Restarting my computer. in the “Storage” I found that Used data has yellow color and described as " system" Now I can’t reach my files. Thank you ;)
If you look to the right of the Finder menu you should see your users name. If you click on it you should see a pull down with your older name visible. You should be able to click on it and log in under that user account. Did that work?
