How can I fix my texas instruments TI-83 calculator? PLEASE HELP.?

I have a Texas Instrumental TI-83 calculator, and whenever I try to put in a certain problem, such as 1/4+1/3, or like, 2 to the second power plus 1/4 or something, my answer is always 1, and it screws me up during tests. Does anybody know how to fix this? Could I have pressed something and hanged the settings on accident? Please hlp, thank you! :)