These are the steps I follow to install PlexConnect on any host:
1. Install your desired theme (github)
2. Install PIL/Pillow (if fanart is desired otherwise skip this step)
3. Choose your desired host to intercept in settings.cfg (I assume you know how to change the host to intercept already)
4. Change the aTV DNS to match your PlexConnect host IP
5. Delete all old prior certs from your aTV and generate new (or copy over the old one's @moody_blue suggested)
6. Ensure you have no running VPN, Virtual Machine software, Antivirus, firewall (if you have a firewall enable ensure ports 53, 80, 443 are properly forwarded), or anything else that could be causing issues you can think of.
7. Reset all network equipment (modem/router/gateways/ethernet converters etc), aTV(s), PlexConnect host's (PC) in your case.
8. Once everything boots back up entirely delete all old certs from the aTV(s), generate new or load the old ones onto your aTV and load the certs into the proper folder .pem and .cer into your desired PlexConnect folder /PlexConnect/assets/certificates/ . (I prefer to load certs via ipaddress/trailers.cer e.g. 192.168.1.101/trailers.cer
9. Once the cert is upload to the aTV reboot it again (helps to clear the cache sometime the aTV needs a little kick to follow the proper DNS to route to your PC PlexConnect host.
10. Once your aTV boots back up and your aTV DNS is set to your PC PlexConnect host all the apps should load on your aTV, if they do this is a good sign, try your hijack and hopefully you will be all set.
IF THIS DOESNT WORK PLEASE USE THIS TO POST A PORPER ISSUE REPORT (copy and paste the template and fill it out entirely):
issue template
Good luck ;)