Something Hard Behind my Plasterboard General problems, solutions, information and advice on fixing to walls of all kinds

[Pukky]

Hello all,

I am trying to put shelf on my plasterboard so i bought metal self driving fixation.

But after while i was unable to screw it deeper, because there was something hard.

I was also trying to find struct by tapping method.

Do you know what it is? And how to proceed?

Thanks!