Q: Back to my mac won't start

I am running El Capitan (10.11.6) on my late 2015 iMac (Proc: 3.2 GHz, Intel Core i5, mem: 8 GB 1867 MHz DDR3)  I cannot get back to my mac to work. When I select it from iCloud preferences its says, "Back to my mac isn't working because it could not start properly" it advises me to turn off back to my mac, restart my computer and try again and I have several times but I always get the same thing. I tried Apple chat and she sent me to the article to set-up back to my mac and then transferred me to another advisor via phone. He ran me thru all the same steps then put me on hold. The call somehow was disconnected and despite asking for a call back number should we get disconnected, he hasn't called me back. It's only been 35 minutes but who's counting. I am open to suggestions since Apple doesn't seem interested in helping me, I need to get this figured out quickly because school is back in and I need to be able to get onto my iMac when I'm in class or at the library. HELP!