HP Pavilion All in One will not power on

[HDoc]

Computer has been stored for up to a year, not plugged in.  No problems with it previously.  Now will not boot up. Nothing happens when I push the power button.  There is a tiny opening on the back of the case, above where the power adapter plugs in.  I believe this is an LED; no light is present when plugged in.

I tried all the troubleshooting steps on the HP website- unplugging peripherals, unplugging the power adapter and holding the start button for 10 seconds.  Nothing happens when I hit the power button and there are no lights on the back of the case. 

This unit worked (slowly) without issue when I last used it about a year ago.  I am now trying to prepare to sell or donate it.  I don't want to spend much on it but I would like to know if I can get it booted up so I can reset the hard drive.  Thanks.

[itsmyname]

@HDoc -- it seems that the computer's power-supply has failed.

A computer technician can remove the disk-drive, temporarily connect it as a "secondary" disk-drive in some computer, and delete everything from the "C:" drive-letter on that computer, to preserve your privacy.

Or, the technician can temporarily connect a different power-supply, to allow the computer to run.

One of the options in Windows 10 is to reinstall Windows. Choose the option to NOT preserve your personal files.

You would still have to purchase a power-supply, before you donate it.

However, I would first check with the intended recipient, to see if they will accept the computer, before spending any of your money.