a line appears when i add type

hi. i've been using photoshop for over two years and i'm currently using photoshop cs. when i add type to my image, a line appears right under the letters like a guide of sorts. it's only a guide as it disappears when i confirm the type. what is this? how do i take it off? my girlfriend uses my photoshop for ten minutes and this happens.

please help.

That's the way it is with CS, Chiho......Nothing to do with your girlfriend at all.