I needed to reinstall macOS, so I deleted my partition and opened the Mac recovery and started downloading Sierra. Unbelievable 6 hours later, the installation was stuck and I turned my MacBook off.
Pressing the power button + Commandcommand R gives me this message:
I tried everything, changing my WiFi authentication type from WEP to WPA/WPA2, all boot shortcuts, resetting SMC/NVRAM.
Pressing power + CommandOption shows me the following:
Clicking the "..." button lets me manually input the WiFi SSID and password, but it hangs forever in the loading indicator.
I don't have another Mac to make a bootable USB stick and reinstall the OS, only Windows.