You have to power cycle the modem when switching the device connected to it. When having problems like now, unplug modem and router, wait at least 10 minutes, power up modem and then after a minute power up the router.
If still no go, look in router status or logs for any hints. Then it's probably time to discuss with your ISP's tech support.
If still no go, look in router status or logs for any hints. Then it's probably time to discuss with your ISP's tech support.