Are You Overlooking the Obvious?
Unplugged or loose network cables are easy to miss yet one of the most common reasons you might suddenly find yourself unable to connect to the Internet. That's not a problem on wireless networks, but on most laptops the Wi-Fi radio can be inadvertently shut off instead. On home networks, it's also possible someone unplugged the router.
Action - Ensure your wired or wireless network hardware is switched on and plugged in.