do you use the wan ip to access the modem from remote site?

possibly try manually set dial number and APN from your ISP. why not send router system log to tplink support to diagnose the problem.

jackychau wrote I have try to upload the firmware TD-W8960N_V1_V3_111108 from the website and try to upload the firmware to the modem, but after the upload the finish, I received the following...

i have no idea of the system log, but i suppose you may try update the modem firmware and test again.

not sure about the compatibility issue, as i can not find the specific dongle on tplink compatiblity list. possibly do a real test before purchasing.

maybe try reset the router, not sure what kind of username password you are talking about though.