@BipBip  Hello, 

1) It is possible that cable going into PA4025P the main powerline unit lost Internet right now,   can you wire a computer directly to that wall cable and see if you could get any Internet from it?

2) If the wall cable has Internet, you could set up  static IP on the powerline unit which is in the same subnet as router, for example :

IP: 192.168.1.200 

Subnet: 255.255.255.0

Default Gateway: 192.168.1.1 (router's IP address)

@GuyP Hello, 

If the Powerline Led goes On and OFF, it is possible the powerline environment is not very ideal or have got some interference ,you could follow this instruction and try to improve the powerline rate: 
https://www.tp-link.com/support/faq/409/           

Please also try a different wall socket for the extender unit , or put the extender unit into the same room as main adapter and see powerline could be stable ON? 

Can you download tpPLC Utlity and check the powerline rate between 2 powerline units and share a photo, thank you. 

https://www.tp-link.com/support/download/tl-wpa4220/

@BipBip  Hello, 

You could also try static IP as suggested above. 

Or try to put 2 units in the same room,  factory reset 2 powerline units and repair them:

• Reset Wireless Powerline unit: via the RESET button/ RESET hole

With device powered on, Use a pin to push the reset hole until all LEDs will turn off and start on again.      

• Reset Wired Powerline unit: 

With device powered on, keep pressing the pair button until most Led flash once           

Later repair them: 

Put 2 powerline unit in the wall sockets, in the same room, and pair them again :

Paring Note:  press Pair button only for 1 sec, Power Leds should be flashing on both powerline units in pairing process. ( if the Power Led does not blink, press it for 1 sec again)
When the Powerline Led or House Leds are on, the pairing process is done