Greetings,
Welcome back to the forum.
I am not a HP employee.
Shut down the PC using the power button or pull AC power.
Restart the PC. Immediately tap "ESC" to get to the Startup Menu.
Select "F2"
Run System Tests.
The HDD may be failing.
A continuing non responsive system startup may require resetting CMOS by removing the CR2032 MB battery. Let the PC sit for about 15 minutes.
Reinstall or replace the battery with a new CR2032 battery.
Check/reseat motherboard component connections for the HDD and RAM.
Try starting the PC with only a keyboard, mouse , and monitor.
Regards