Be sure you can connect to
Github.com, clear your DNS cache for that.
WIN + X -> PowerShell with Adminrights
If it's not working, try to set a new DNS nameserver. Like Cloudflare.com (fastest one)
WIN + X -> PowerShell with Adminrights
PowerShell:
$adapter = Get-NetAdapter | where {$_.InterfaceAlias -eq (Get-NetRoute -DestinationPrefix 0.0.0.0/0 | Select-Object -ExpandProperty InterfaceAlias)}
Set-DnsClientServerAddress -InterfaceAlias $adapter.ifIndex -ServerAddresses "1.1.1.1, 1.0.0.1"
Clear-DnsClientCache
I wrote a script for you which automatically selects your adapter and sets the DNS server for it.