Quick photoshop question

Houston we have a problem

I didnt mess with no settings at all in PS…and now, when I make a new image (500 x 500, 8 bit, rbg or cmyk all the same…) I get locked background?

Why and how to unlock it?

I tried adding a new layer, but when I flatten it, it goes to locked again…

It never happend before in my PS…how to undo this?