umm, seems weird. You can contact support@tp-link.com

What's the signal strength on your computer? And the link speed showing under internet connectivity? If the PC is also very slow when connected via LAN, restart your computer, and test the speed when...

I don't find the model TG 3831. You can find instruction about how to set up the CPE520 on the tplink website, or refer to the installation guide.

The LAN IP address of the extender is 192.168.0.1, you need to change it before changing the range. What's the light status on the extender? If there is no internet from it, the mac address or Ip...

It's a bit confused. I don't understand how you want to connect the C50 router and a range extender along with the freebox router. The C50 router is wireless also, so you may try WDS, linked to the...

Access the extender http://tplinkrepeater, you will find DHCP server. If you cannot access it, find out the IP address of extender on the router and use the IP address to login the extender.