Strange hammer error

Hammer was working fine yesterday but when I got on it today and click on anyting (Brushes) it makes it bright red and covers the entire brush while it is selected. Props also disapper whenever i deselect the brush their on, and whenever I move a little window pops up with a 3D image of my map except a little darker (Lighting preview window). When I close it and move again it pops right back up. And the trees… The branches look like balls of bark instead of a branch.