update the router firmware to the latest one ,reset the router to factory defaults and try again. disable the pin on the usb modem and make sure it can work properly when plugged directly into the pc.

what if you disconnect the 3G device, set wan only, can you get wan ip address automatically?

did you try open the page with 192.168.0.1? check the ip settings on the computer, open control, panel, network and sharing center/network connections , change adapter settings/manage network...

have you checked the bin file center on tplink website? http://www.tp-link.com/en/support/3g/

what 's your wan connection type and wan ip address on the router?

the product you have is a modem router, i suppose what you need is sth like a repeater, such as TL-WA901ND. there are also some nano models like TL-WR702N/TL-WR700N which have the repeater mode.