Hello Netsanet eyayu

If your HP LaserJet Pro 400 M401 printer is not turning on, there could be several possible reasons:

1. Power Supply: Check if the power supply to the printer is properly connected and if the electrical outlet is working. Try connecting the printer to a different outlet.
2. Power Cord: Check if the power cord is damaged. Try using a different power cord or borrow one from another working printer.
3. Circuit Board: If the printer still does not turn on after checking the power supply and power cord, there may be an issue with the circuit board. This could be caused by a blown fuse or other internal component failure.
4. Printer Control Panel: Sometimes the printer control panel may be locked or unresponsive, preventing the printer from turning on. Try pressing and holding the power button or unplugging the printer and plugging it back in to see if the control panel resets.

If none of these steps work, you may need to contact HP support or a professional printer repair service to diagnose and fix the issue.