App store not working, having hard time with sierra solution to this problem

GIGABYTE LGA 1151 Z170 HDMI 2-Way CrossFire ATX DDR4 Motherboards GA-Z170-HD3 Core i5 Geforce 1050ti

Headline says it all; can't download, can't access icloud, the problem seems to be starting after I use a time capsule to migrate all my files. All fixes on this are very old or in german and also bricked the computer.