If you are using both ethernet port on the modem for router and play station you can get internet on only one device so please disconnect the play station and the router then restart the modem for a minute then connect only the router to the modem ethernet port where the play station was connected to the modem before, then check for the WIFI. 

This is the situation , even though you have 2 Ethernet ports on the back of the modem , you will be able to connect one device at the time and the reason why its because the modem is getting just 1 valid IP address. If you want to use both ports at the same time you will need to contact your ISP and request a secondary IP Address