First you need to find out what you have on the roof. Is it a DishPro (twin or Quad) I assume you are trying to get 110 - 119.
Let me put it this way - If you are using Twin LNB's (two outputs) then all you need to do is run a second coax, but this is all guess work because you haven't provided enough information.
Here is the info neede:
What type of dish? Your location? Type of LNB? Switches (if any)?
with ONLY 2 receivers and ONLY 1 Dish Pro TWIN LNB..just run cables DIRECTLY from the 2 outputs on the LNB to each receiver (use NO switches)...then go into your receiver menu, and antenna/dish settings and input..
LNB type...dish pro (DP) freq... 11250 disque #1- 119 disque #2 - 110 22- OFF power ON scan all etc..
Of course U must have good working hardware (cables, cnnections, LNB's etc), the dish aligned correctly, scans performed lately, latest bin loaded, correct keys inputted, and receiver rebooted..then watch TV