Question: I realize this has been asked before and I have read as much as I could find on the topic but I still need help with this because there are so many different approaches and the ones I am trying aren't working.

So I have 2 routers, lets call them A and B. Both have a wireless feature and are active. A is in the basement and receives the internet. There is a TV on the ground floor that is connected to A through an ethernet wire. B is upstairs and gets the internet from A through an ethernet wire. Connected to B, is a desktop running Plex Media Server. 

What I want to do is make sure devices connected to both routes can access the Plex Media Server. 

So what I have read is that I should plug in the ethernet wire connecting B to a into a LAN port instead of the WAN port. After that I should turn off DHCP. I have tried this and B stops receiving internet. What am I doing wrong?

Another thing I have read is to use Router B in bridge mode but Router B is running openwrt and I have QoS on it so gaming/VoIP/browsing is unaffected by heavy downloading/uploading. I would prefer to keep this active. I realize it might be ineffective if a device in Router A is doing some hardcore downloading but all that stuff is done on Router B anyway so it doesn't matter. Router A can't get openwrt because it is a shitty one provided by Bell.

So, how do I proceed with this?

Answer: 
When you plug into a LAN port and turn off DHCP on B, you need to give it:

* an address on the A router (B's LAN address - probably by default they are both 192.168.1.1, given how common that is, and they can't be the same if they are on the same network.)
* Router A's address as the gateway address of its LAN settings (which probably defaults to itself.)

If not, it won't work.

If we assume a typical dreadful default setup (which may not match your actual default setup - feel free to post more details about what the settings actually are) you would have both routers set to 192.168.1.1 and both handing out 192.168.1.100-254 for DHCP (or 192.168.2-254 for the most dreadful default of DHCP.)

These settings can, and should, be changed.

Keeping the changes minimal: 

* Leave A at 192.168.1.1
* Set A's DHCP to 192.168.1.100-150, unless you really expect more than 50 devices.
* Set B's LAN address to 192.168.1.10, and its gateway to 192.168.1.1
* turn off DHCP on B *or* let B hand out 151-200 (make sure it hands out 192.168.1.1 (or whatever A is set to) as the gateway, as well)
You need to use Router B as your main and Router A has to be in dumb modem mode.
The way you do this is:

1) Router B <--> Router A Wan-to-Lan wired connection

2) insert PPPoE information in router "B". in which case, router B handles everything, PPPoE to the internet, and internal DHCP

optional: disable DHCP and Wifi On router A. no clients should directly connect to router/modem A.