Thank you guys for all your help - but the Tivo ended up being fried. However, I still have a wiring problem, but I think I've figured it out. What follows is my wiring diagram and what I think is the solution at the bottom. I'd appreciate confirmation of my solution (or that I'm wrong). Thanks!
Direct TV dish, round, 2LNB, both lines to a Samsung 3-to-4 multiswitch. My regular antenna is on the third lead into the multiswitch.
From the multiswitch to the living room is one coax cable, 50-footer, to a Holland STVC splitter that has a specific output line for the dish and one for the antenna. From there, coaxes to the dish, the DVR, etc. This setup works like a champ.
From the multiswitch to the back room: one 25" coax (which is actually too long, but is what I had - it will get replaced with a shorter one). This goes to a RadioShack satellite combiner, along with the antenna wire, and then a 50-foot coax into the house. From there to a RadioShack satellite splitter, with the antenna going to do its thing (and working perfectly) and the other to the receiver. To see if the problem was in the inside splitter, I took the line coming into the house directly to the receiver - still nothing.
Looking at my set-ups and based on what I've read that ya'll have sent me, please let me know if I need to do the following:
buy another multi-switch to use to combine the antenna and satellite lines on the roof instead of the regular combiner
and
buy another splitter like the Holland that is specifically labeled satellite and dish
or
can I get away with just the new interior splitter and not have to crawl on my roof again? I really hate that part.