How about upgrading the firmware? You tried g.dmt? If it won't help, check the replacement procedure in India here. http://www.tp-link.in/support/rma/

The printer cannot obtain IP address automatically as the windows, mac etc.? If so, why not change IP settings on the printer directly? On web interface of D2, go to DHCP Server---Address Reservation...

When connection drops, how about status of ADSL light and Internet light on W8980? You'd better ask your ISP to check if they made some limitation on their end when you use a brand which is not given...

Follow the guide as below to restrict the hours your daughter uses the internet. http://www.tp-link.com/en/faq-467.html

Internet light on the router is on? Other wireless clients and wired connection are all working? On the iphone, if you cannot access internet, can you login http://192.168.1.1 which is your router's...

Did you try chipmaker's driver? Contact TP-LINK support and ask for it to try. http://ticket.tp-link.com/index.php?/Tickets/Submit