Last answer looked good but just to be a little more concise: 1) Verify all power cables and video connections are good with no bent pins. 2) Try replacing the bulb, but before installing the new bulb verify it is the correct wattage 3) Try replacing the Lamp
If the unit can not seem to focus no matter how much you adjust the lens please verify that the lens itself has not been scratched or damaged. If the lens is in good working condition then unplug the unit to remove power and wipe the lens with a cleaning cloth and a little bit of lens cleaner. But please be careful not to use too much cleaner because harsh chemicals will damage the lens. You can also replace the lens cover if the lens cannot be cleaned by hand. Lastly verify the actual connection of all the video wires and if they are secured correctly try using a different video wire to verify the unit's video wire has not gone bad.
Thats good you checked to make sure you had the power cable plugged in and it was a good outlet because that is the initial troubleshooting step. Next try to clean out all the vents and filters because an accumulation of dust can cause the projector to not turn on. Following this logic verify that the cooling fan is functional and cooling the unit properly, the build up of dust and poor ventilation can cause the unit to overheat and if the fan is not properly cooling the unit and it overheats it will not turn on. Lastly if the unit is plugged into a good outlet and well ventilated and continues to not turn on you will need to replace the main board.