Paint Terrain problem

Hey guys,

So today I don't know what happened, but ever since I tried changing detail resolutions and editing grass by unchecking billboard. All of my grass disappeared from my terrain and when I try adding more grass on pre-existing ones, it erases it instead of adding more. I've tried uninstalling unity, opening a different scene, everything, but nothing worked! I tried adding grass on a scene I haven't created that contained grass, and still, the grass was getting erased than getting added.

I am able to add trees, rocks, and paint textures though, but not details. Did I press something that causes this?
Also, "draw" is checked in terrain settings.

I don't know what I did, please help someone ASAP as I need this for my homework assessment.

 

Never mind, I'm so stupid.
My target strength was at 0