Depending on what is going on.....
If you haven't finished the current course, it will be greyed out until you finish that section.
If you are not up to date on your tuition payments (if you aren't lucky enough to have paid in full the entire semester), they will be greyed out as your account has been put on hold.
If the exams you are referring to are the Proctors, you won't be able to take them until your proctor receives them and you take the paper tests. The proctor then mails them back and you get the grade.
See attached image....
I am just not sure what exactly you are looking at, just going off of what I know from my current courses and experience. Hope that helps.