You don't give us much information, but I've finally learned that the best first-aid for practically any situation is to power-down and unplug the devices involved for a short time (10-30 seconds ???) and try again. Then go to the more advanced remedies. In this case I think I would remove and re-install the printer for wirelss operation.
Yeah this could be nothing more than your printer has a static IP stored in it and your router, when it restarted dumped it's reservation and has assigned it's IP to something else. Hard to say without more information.
Need printer name and model, computer OS X version, Router name and model. Or you might get luck and rebooting everybody will fix it - which it most often does.