First of all, figure out whether the problem lies at your end or ISP’s. If without intervention from you or your ISP (Internet Service Provider), the connection starts to work again, then most certainly the problem lies with the ISP. And what you’re experiencing is commonly known as a service outage.

Service outages for residential  users are common occurrence. that’s nothing you can do about it. You may complain to your ISP but in the short run, it’s better you just try and work around them.
The way to go about it is, after a service outage, switch off your DSL or cable modem, wireless router, if you have one and your computer, and then back on again after approximately 10 seconds in the above order.