You accidentally turned on an application that lets you solve inequalities.
To turn it off, go to:
Apps-->Inequalz (number 7)
A prompt of whether or not you want to turn it off may come up.
I've had this TI-84 Plus for about two years now. A couple of months ago, some unknown problem occured which makes it unable for me to view multiple graphs at once in my graph window. When i input more than one function into the "Y="-(aka "STAT PLOT") button, I have to >mark< one of the "="s in front of the specific function i want a graph of. It's not possible to mark more than one "=" at the time, which makes it really hard for me to compare graphs etc.
Sorry for my bad english, just ask me if something is unclear. Help would be really appreciated.
PS. I've tried to reset it, though without result.