A simple task, I know.

The GFI in my kids' bathroom went bad.
I installed the new one. When it's hanging out of the wall, it works.
When I push it back into the box and press the button, I get sparks
and it trips the breaker in the basement.

The damn ground wire keeps popping off, no matter how hard I torque it
down.

All the other wires stay intact...they're the type that plug straight
into a hole in the GFI, then a screw tightens them in.

What's the trick for getting the ground wire in tight?
There's a little metal plate, but the wire doesn't fit under it...so
I'm just trying to tighten it under the screw head.