Two basic things:
1. Reboot the Internet connection i.e., unplug any and all cables Internet has to your computer, including power cables. Also unplug the router's power cable --- the whole system, that is, although you don't need to unplug but one end of a cable. Wait for 30 seconds, then plug them in the order "first comes first" etc... this is not a question of lethal importance, but connect the router first, your computer last.
2. If it won't help, right click on the Network icon in your taskbar, and choose "Troubleshoot problems". It'll give something.
Plain first aid, this is.