This is going to be a bit long as it sounds like you're talking about three different things.
First, is accounts. Unless I misunderstand what you're saying, your Site Admin is not a role, it is an account (I say this because you said you login to it...that's what you do with accounts). Just because you name it Admin doesn't give it site permission. By default, every one is Authenticated User which has permission to only view/enroll/participate where applicable.
Second, what do you want the account to be able to do (role)? If you have created a custom role, great, if not, it sounds like Manager might do just fine (unless you don't want them to be able to create accounts, courses, etc...) and I've added directions for adding a person to the system roles list (below). If the role you want doesn't appear on the system listing, you can add it or you can customize a current system role. Student and Teacher are not considered system roles and I do not recommend adding them but you can (you do this by editing the role and checking the system box).
Third, I think you're either talking about a) the My Home (Dashboard? in 2.9) page or b) you're going to a category where there are no visible courses. A) My home is when you login to a new account, no courses are assigned to it unless you explicitly enrolled the account in a course or courses before the login. System roles (and category) mean you can access accounts without being enrolled. You would need to search for the course(s) you want to work on. B) If the problem is visible courses in category, the role that account is assigned may not have permission to view hidden courses.
When you create a new account, if you want it to have site permission, you have to tell the system.
In Site Administration (from an account with actual Admin or Manager permissions already assigned), go to Users->Permissions->Assign system roles. Click the role you want a particular account to have. Search for the account on the right, select it and click Add.
So, here is my example:
I have people who need to be able to enroll staff, request courses, add content to courses, view all courses on my site and have access to them, view grades and reports and view courses from other roles' perspective (like participant).
I created a role called SD Professional (Staff Development) as a System and Category role. It allows all these things and some more...like viewing hidden courses. It is not a graded role and doesn't allow real participation in most activities (quizzes can be completed, but only as a preview and doesn't ever show up in grades).
I assigned all the specific staff accounts to that role at the system level.
They can now request courses and view any course on the site. If they want to enroll users or add enrollment methods, they switch their role to Teacher and engage in those tasks. If it is a course they generally control (we have courses for all staff and courses for specific sites...site staff control their courses, I control the all staff courses), they can explicitly assign themselves the Teacher role. And they can see hidden courses.