In the years that I have been supporting and repairing printers, I have found a few steps that you should always try first. Some are in HP documentation but often overlooked, some are just tips you pickup. But if you have a problem with your printer, trying these things first might save you having to post and an expert as you to try these things anyway.
These tips are all related to power issues and I have had them all happen at one time or another.
1. Perform all testing with any USB or network connections unplugged. You want to confirm that the printer is working before adding possible computer issues to the mix.
2. When turning the printer on, listen carefully for any fans or other noises. Often a failed display screen can make you believe you have a power issue when that is not the case.
3. If your printer is not powering up or is acting erratically the first you want to do is make sure you have good reliable power. This means heeding the instructions in the manual that state "DO NOT PLUG YOUR PRINTER INTO A SURGE BAR OR MULTI-OUTLET STRIP." Most UPS devices cannot support a laser printer and will causes errors. There is a reason for this. Most printers, even small desktop laser printers, will try to draw more power than these outlets can provide. Turning on a laser printer creates a surge, which these bars are designed to filter.
4. When diagnosing a power problem, unplug the printer and leave it off for at least five minutes before plugging back in. Some devices have a reset device that will reset only after power has been disconnected.
5. Always try a different outlet if the above steps do not resolve your problem.
6. If the above steps fail, try a different power cord. I was as surprised as anyone when I found a customer with a bad power cord, but I can confirm, it does happen.
If running all the tests above you still have no power, then likely you have an issue with either the power supply or one of the controller boards in the printer.