Flashing cursor on TI-84 Plus?

I haven't used my calculator since the AP Calc test, so I don't know specifically when it happened, but now when I turn it on, I can't do anything.

At first the screen just flashed "Ans^-1" (but the actual display of power of negative one) over and over, like I had selected it, but no matter what button I hit, nothing happened. I pulled out the batteries a couple times, waited half an hour, but nothing changed.

Then today I took out the backup battery as well, which did a little. Now it just flashes over an empty space, like when it's waiting for you to type the first number, but I still can't do anything with it. Help?