For a number of reasons, your device (computer, smart phone, tablet, smart TV, etc.) likes to be restarted. This includes both restarting (a.k.a. rebooting), as well as shutting down (a.k.a. powering off) and then powering back on.
This cycle clears memory, flushes cache, closes all running programs, as well as many other tasks, all which may very likely fix the problem you are having.
Believe it or not, many many many....many times, we find devices are not turned on. You can usually tell that a device is not on by an indicator light.
Confirm that it is on, and if it isn't, turn it on!
Double and triple check that all power cables, network cables, and "whatever-else" cables are plugged in correctly and firmly.
Power cables: you can typically confirm that they are connected by turning the device on, or by some light indicating the device is on and powered.
Network cables: you can typically confirm that they are connect correctly by listening for a click when inserting them. Also, if they are properly connected, you should notice lights flashing near the insertion point.
Monitor cables: make sure they are pushed in all the way. If they have screws on the connectors, screw them in.
Printers and other devices: many devices use USB connectors. Try plugging in to a different USB port on your computer.