Frustrations

So I had to take a test so that I could be accepted into the degree program at OU. Everything went well with that and I got my email just a couple of days ago saying that I had meet their standards and I was in. This of course made me happy. Then I went to enroll into my upper division courses and low and behold they are all full. Ugh! So I contacted one of the professors of these classes.(There are four of them that have to be taken all together at the same time!) He tells me that it won't do any good to just show up and try to get in to the classes that I need to put myself on the waiting list and just see if a student drops out. Blah! Why can't anything be easy with this college?