Your Hub Server is a mini computer that looks like this:
This device typically sits BELOW the counter (usually on top of the cash drawer or to the side of it). The ELO touchscreen monitor (the POS you interact with) is a separate device that gets plugged into the Hub Server - the ELO monitor (and therefore the POS) cannot function without the Hub Server. You can think of the Hub Server as "the brain" of the system.
For the sake of comparison, this is what the ELO touchscreen monitor looks like:
So when we refer to the "Hub Server", we're talking about this device here:
The blue light means in the photo above means that the Hub Server is powered on. When it is powered off, it looks like this:
How to restart the Hub Server
If you ever need to restart your Hub Server, just hold down the blue button for 3-5 seconds. Then release the button and confirm the blue light has gone out.
Once you've done that, just press the power button again to turn it back on and verify that you see the blue light.