My Screen Just Went Black and None of the Equipment is Responding!
When this issue has come up in the past, it's been Point of Sale units being shuffled around in the work area and cables being loosened up from where they've been plugged into. Ideally, you don't want to have cables stretched to their limit anyway, because besides knocking cables loose, strain on cables will break down wires inside and cause premature failure of the cable over time, so avoid that situation where possible.
Bear in mind that any completed transactions are still saved in Trackside previous to anything that was being worked on when the issue occurred. Once your point of sale is back up and running, you may resume your till where you left off and the details of all the transactions will still show up in any of your reports, including closing till.
You can check to make sure your PC still has power. The power lights aren't overly prominent on these, but they can be seen if you look through the vents or at the top panel. Your particular unit may differ slightly from what's pictured.
If you don't have power, you can try reseating your power cable both at the PC and the wall.
If you do have power, the PC may be ok, and we may have a monitor issue. Reseat the HDMI cable at both the PC and monitor first.
If there's still no display from the monitor, check the power light on it to see if it has power.
If the light's out and it can't be turned on, check the monitor's power cable both at the monitor and at the wall.
If the problem still exists, check My Computer Just Locked Up / Won't Turn On for more steps.