You cannot power on the laptop by using a key on the keyboard.
The only way to power on the laptop is by pressing the power button.
However, if you have advanced BIOS on the PC, try the steps recommended below.
1. Turn off the computer and wait five seconds.
2. Press the Power button to start the computer and repeatedly press the F10 key to enter the BIOS setup menu.
3. Use the arrow keys or select power tab from the page.
4. Select Power On By Keyboard from the list and specify the key.
5. Press F10 to save changes and exit from the BIOS page.
Lastly, you can contact HP support and get the service options for your laptop.