If I understand the issue correctly. You had an instance of SQL setup, on your computer. Replaced the OS, installed a fresh version of SQL Server, and attached the database to it. Now on connecting to the SQL server (That completes succesfully) however, when trying to access data in your OMSDB database, you get a denied message.
This seems to be a permissions issues. At the very least you will need to grant to the user account db_datareader. Though its also possible that if the user login was recreated at the SQL server level, its SID is out of sync with the database user. in which case the system stored procedure sp_change_users_login will need to be run on the user (in the OMSDB database).
EXEC sp_change_users_login 'Auto_Fix', 'user'