During the installation itself you are asked how to login - via Window authentication (who you are currently logged into Windows as) OR SQL auth. I always choose the latter and put in the sa account as the user, even if it means the IT guy has to remote in and type in the password for me.
Otherwise, in SQL Mgmt Studio, login there as the same exact user you used during the installation (same Windows auth vs SQL auth . Then click on New Query and type in:
CREATE DATABASE MAS_SYSTEM
If you got an error then note the error and troubleshoot that. It may or may not have anything to do with permissions.