I was successfully able to do an upgrade on 1 of my 2 C7 Pro hubs to a C8. After it came back online, it had changed to a different DHCP assigned IP address. I want both my hubs to be at defined fixed IP addresses, so I attempted to set this one to fixed. Long story short, after doing so I can no longer reach it either directly on my network or through remote access.
So is there a way to HARD factory reset the hub when you cannot access it to allow me to start over?
I doubt you need to do a hard reset. Sounds like you just need to reset the network settings.
That said, powering up your old C7 after having migrated to another hub can be problematic also.
(Click on what do I do with my old hub)
Directions for doing a full reset are in those directions. (NOTE: DON'T SKIP STEP 1 IF YOU HAVE A SUBSCRIPTION ON YOUR OLD HUB)
Thanks for the reply. I've finally gotten back to this. To keep my system running, I had to revert back to the C7 for the hub I was trying to update. I have two and the other is the Master hub so i needed them both running smoothly.
As far as the issue and doing the network reset above, you must be able to access the hub via the network to be able to do that reset, which is essentially a soft reset. Since I can't access the hub right now at any address including the one showing up in my router, I wanted to factory reset it so I can start over.
Try the Network Reset again. Then search for its NEW IP.
You should then be able to connect (at least thru maintenance port.)
On the bottom of the hub, there is one opening that looks slightly different than the rest. There is a physical Network Reset button in that one hole that will reset your hub to DHCP network settings. Hold the button for 7 seconds (the LED light on the hub will change colors) and then wait for the hub to reboot. Afterwards, you should be able to 'see' your hub in your router's DHCP leases. Once you know the new IP address, connect to it via a web browser and then you can perform whatever type of reset you'd like, typically via the HUB's Diagnostic tool. It is all covered in the official Hubitat documentation that @tray_e mentioned earlier.
This is EXACTLY what I needed. Thank you!!!
And included the same picture..... 
Download the Hubitat app
