I have 2 accounts on my windows machine and I was experiencing this problem with one of them. I did not want to use the sa
account, I wanted to use Windows login. It was not immediately obvious to me that I needed to simply sign into the other account that I used to install SQL Server, and add the permissions for the new account from there
(SSMS > Security > Logins > Add a login there)
Easy way to get the full domain name you need to add there open cmd echo each one.
echo %userdomain%\%username%
Add a login for that user and give it all the permissons for master db and other databases you want. When I say "all permissions" make sure NOT to check of any of the "deny" permissions since that will do the opposite.