I can't use the brush to "draw" my 2d level!!!

I had a problem, i lost my level and the player in the scene (I unzoomed a lot) I found that if I select the player and press F it appear on the scene.
The problem is that I can’t do the same for the level I already drew and I can’t even draw a new level; the grid disappear and i can’t draw when I select the brush tool!

Update: When I try to make the level appear by pressing F, there is just a white line on the scene???