contact TP-link support for some help. https://www.tp-link.com/en/contact.html

try to use different device to login, if still no good ,reset the modem router

Hi there, you can refer to the UG for some help, pay attention to page 100, and page 101. https://static.tp-link.com/res/down/doc/TD-W8968(EU)_V4_UG.pdf

Hi friend, you can not upgrade the firmware in different country, it's speical designed.

try to reset, and do you have other power adapter, it might be the problem of the power adapter, try with a differnet power adapter, and test if you have the same issue, if yes, check if still in...

try to reset the device and reconfigure it, if the same thing ,check if it's still in warranty for Repelacmeent.