I have bought Hubitat c-8 through reseller. After unboxing I was following the setup, I connected hub with Ethernet cable to my router and connected to power. But hub is stuck on blue light, it has been 30+ min and no luck.
Let's try this. First look on the bottom of the hub, copy down the MAC and create a DHCP reservation for it on your router. Then find and press the network reset button for 7-10 seconds.

If that doesn't resolve anything try to see if the Diagnostics Menu is available
http://<IP address you made the reservation for above>:8081
If it is, select Soft Reset.
Actually, I spoke too soon. After pinging Hubitat on LAN and hard resetting, it seems to be working correctly now. Can close this.
You may want to go into the Diagnostics Tool and do a FULL RESET (in advanced) if you have not gotten too far in setting it up yet. This will be sure everything from the prior owner is wiped off it.
Following two consecutive power outages, my C-8 will no longer start up. It is stuck with a blue light and is no longer connecting to my network (hardwired). I can't access the diagnostic menu due to a lack of network access. I tried resetting it by pressing the button on the bottom without any luck. Any suggestions will be appreciated.
The eMMC may be hosed as a consequence of power interruptions. If you have Hub Protect, you can put in a warranty claim.
How did you verify this? On the router admin?
Did you check the link lights on the router/switch port? Is it showing any signs of "link"?
Did you try a different ethernet port and cable?
Problem solved with help from the Facebook User group
Not going to share that solution for future users?
EDIT: I found it in the group, hub apparently was setup for both ethernet and Wifi, and had connected to the Wifi only for some reason. It should have also connected to the ethernet though, so might still be an issue with the port or cable.
Tip: You should not leave the hub connected to both ethernet and Wifi, if using ethernet disconnect the Wifi.