TI-89 Problems

When i go to do a cos, tan, sin function or add an exponent (ie. 2^2) the calculator wont answer me. It just repeats what i have typed into it on the main screen without actually doing the tan function or squaring the number. Please help me. Is there something i need to change in the settings? Basically it just wont solve things and repeats what i have typed in right back to me. Basic functions like plus and minus work but that is about it.