Television "locked". I was watching television last night and changed channels. all of a

Question

I was watching television last night and changed channels. all of a sudden, the screen went blank and it said locked at the bottom. I do not have the remote that came with the television, however, i use a universal remote that has always worked. I cannot get it to unlock. ( I don't even know how it locked, since i do not have the remote with the "lock" bottom on it.