Question on finding studs
The outside corners of your walls have metal "drywall corner bead". (There's also paper and plastic.) Sometimes, though rare, there's metal bead in the inside corners. 

The corner bead itself is relatively thin, but if you're trying to get through it, either with a drill bit or a screw, you'll need to push reasonably forcefully. If you don't, the bead can ride up the screw or bit, which will create a crack in the plaster. 

Putting a screw into the last inch of a corner isn't a fabulous idea, though. Typically, there's 1/2" drywall, which won't hold a screw, and then the edge of the stud, which can splinter off and not be very strong.