When I open the Google Play Store it says, no connection retry even when I am connected to wifi and when I hit Sign In in the Youtube app it says, An error occurred.
You checked your internet connection of the modem/router? I also got that problem several times.. > modem/router/ap restart helped me in this cases because it was a connectivity issue with my provider and not an android/app problem. Sometimes even a simple turn into flight mode and back resolves this issue (at least for me).
Some times your network blocks ip's or google may black list your network ip's for some reason.. If setting date and time, clearing data and cache doesn't work. Install VPN HotSpot Shield via browser. Than turn this app on once it secures your connection you will be good to use play store.
Hope this helps.