Car wont start

I have been having a problem with starting my car for about two weeks now. When I try to start my car the lights on the dashboard light up and the stereo and everything works, but when I try to turn the key to start the engine the entire car shuts off. If I take out the key and try in a minute or so it does the same thing. I believe the problem is with the positive contact that connects to the positive terminal on the battery because if I take this contact off and sit it back on the terminal the car starts up fine. The contact has a crack in it also that makes the contact not sight tightly on the terminal to the point where i can basically slide thecontact off of the terminal. I am no where near an expert on car maitanance but from what I can conclude it seems like that may be the problem. Plus this only started happening since the crack was formed when I was tightening the contact onto the terminal after I had taken my stereo out to clean it. Hopefully you guys have some information. Thanks.
ps- my car is a 1991 Camry 4 cyl.

I recommend getting a battery post and terminal cleaner. They're relatively cheap at your local auto parts store. You should clean the posts and the terminals first before jumping to conclusions. If this don't correct the problem, then you'll probably need to replace the terminal, or the battery.

I think you'll have to replace the cable.