I have installed PostgreSQL 9.6.2 on my Windows 8.1. But the pgadmin4 is not able to contact the local server. I have tried several solutions suggested here in stackoverflow
I ran into this issue as well. Windows 10. I had older version of pgAdmin 4 (1.6) and 2.0. I guess both are older now.
In any case a complete uninstall of both versions and a reinstall of 2.0 worked.