The 3G/4G router does not support WIMAX.

First of all, check if your modem is on its compatibility list www.tp-link.com/en/support/3g-comp-list/?model=TL-MR3220&location=1205; as to the unlisted modem, there might be possible compatible...

First of all, connect your computer to the router's LAN port by cable; then pick up the default gateway by ipconfig. Then try to login to the router's configuration page with the default gateway...

The latest firmware does not work for me as well :( The other day i tried my luck to send an acquiring email to TPLINK support. They told me they are still working on this issue. So i am waiting for...

I don't think there is other fix on this. The router must be faulty now. What a pity!

Did you use wifi connection while you upgrade the router? And is there a power off on the router during the upgrading? Even if the hard reset won't help. I am afraid yours is damaged by upgrading.