I worked for a while for an internet service provider and this happens to modems a lot, either when you turn unplug them to re locate or to clean, or when there is a power or outlet failure.

when the modem turns back on it pulls up all the info from the main router and loads its saved configuration but sometimes the configuration does not load completely and it doesn't generate a proper IP address for the computer to pull or it does not load the user password configuration for the modems memory or WIFI memory.

There are a couple of things that can work to resolve without full reset.

1. select the WIFI network on the computer and click on forget network and try and connect. by entering the password again. (if fails try option 2)

2. Disconnect wifi on the computer then turn router off for 30 seconds or so then turn it back on and try to connect again. (if fails combine with option 1)

Normally this forces the modem to recognize the devices again, but if the memory is not loading the information even with this then the last resort is to reset and let it load the settings.