Try to disable UPNP or configure Bandwidth Control.

In your screenshot, under Multiple SSIDs Settings, there is Use WPS but No is selected. Is that what you are looking for? Where do you see that you have to enable WPS to install chromecast?

Is it connected to USB port of W9980? To make printer server function work, you have to install printer controller utility which is only compatible with WinXP/Vista/7/8 and MAC.

Can you login web interface of D9? Go to operation mode and select Wireless Router Mode. Connect the modem to its LAN4/WAN port and connect PC to one of LAN ports. If your modem's IP is in the same...

Try to configure DNS 8.8.8.8 manually on the phone to see if it helps. Any other web browser on the phone to try? What's the firmware version of your router?

Are you connecting the laptop to one of LAN ports of WR740 and connect the modem to WAN port of WR740N? There is no direct connection between the laptop and modem, right?