If you has the US firmware, then you cannot update it to other non-US firmware. It's okay to use US firmware, no big differece, just some different on Wireless Channels on 5Ghz. If you can use the...

Do you guys try reset the router to factory settings?

I think you'd better submit a ticket to TP-Link support for this issue. http://www.tp-link.com/en/support-contact.html#E-mail-Support

What's the LED status on the two powerline units? Make sure the house lights are lit up on both, if they are off, pair them with instruction here: http://uk.tp-link.com/faq-1617.html

Do you have the latest firmware? If no, you may have a try:o http://www.tp-link.com/us/download/TL-NC450.html#Firmware

Hmm, looks like TP-Link has removed the function.