Frozen App

I am a novice in Excel and my spreadsheet and all Excel functions are frozen by the appearance of a pop-up that includes a GoTo field first and a Reference field below that . I am guessing that this box is part of creation of some formula(?) but I have no idea how to clear it. It will not cancel, delete, or "x out"; I rebooted the entire computer hoping to reset but it didn't work and it has locked up everything. Is there a way to cancel this action and save my open spreadsheet?

JT26