Numerous circumstances can cause your network to go dark. Follow these steps to fix it. (These tips presume trouble with wireless networking but largely apply to wired networking, too.)
If you use a USB-connected networking device, unplug it and then plug it back in. USB Wi-Fi sticks are notoriously finicky.
Next, reboot your router by unplugging it, waiting 30 seconds, and plugging it back in. You may want to reboot your system while you wait. This procedure will fix the vast majority of lost-network problems.
Didn’t work? See if other PCs on the network can access the Net. If not, your ISP may be having an outage. Try rebooting the cable or DSL modem.
Check your machine’s IP address to make sure that the router is properly configured. Choose CMD from the Start menu (type CMD in the search box to find it quickly) and type ipconfig /all. From there, find the proper adapter (you may need to scroll up) and look at the ‘IPv4 Address’ item. If you have a typical home setup, the first three numbers (separated by periods) should be the same as those of the DHCP Servers. If not, you may need to reconfigure or reset your router, which could have become corrupted.
If you’re using Windows Firewall (or another software firewall), it might be interfering with network access. Try turning it off (you can find Windows Firewall in the Control Panel).
Finally, if you’re on a wireless network, try plugging in an ethernet cable and connecting your computer directly to the router. If this works, you likely have a problem with the wireless adapter’s driver. Try updating the driver manually by downloading it from your computer manufacturer.
Other common problems with Windows PCs can also be solved with 5-minute fixes.