Hi, make sure a stopcock or isolation valve hasn't been turned off on the mains pipework going into the tank inf the loft. Check the ballvalve arm isn't stuck and moves up and down freely.
Hi, the tanks should be filling via the incoming mains supply through the balvvalves.
Check that no one has turned your outside stopcock off by mistake
Hi, if your header tanks are empty as you said there is an issue with the mains water filling your tanks . It might be better calling your water board and they should come and check