My ISP often loses connection to its DNS server. Confirm i you are connected to the internet by opening cmd and type:
ping 8.8.8.8
ping google.com
if the 1st is successful and the 2nd fails, then you dont have a working DNS server configured. You can set the DNS on your PC if you configure a static IP address.
Next while connected to the network, run ipconfig /all
make sure your IP address on the wifi or ethernet adapter matches your router IP subnet. If it starts 169.254.x.x then your not getting an IP from the router. DHCP may be disabld - enable it, or set your IP manually