HP Envy Phoenix 810-370st won’t start

[Tefy-721]

My desktop won’t start up. 
all cables are connected. Light green is on, on the back. 
screen on monitor is black and it only goes on for couple of seconds saying that there is no signal and it goes off. 

couple of days ago there was a power outage because of a car that crashed on the pole that provided this apartments power. (When that happened the computer was off) 

not sure what the problem is, but before this happened every time that I turned the computer on the fan will turn on as well as a red light on the front. 

any ideas? 

[Lil_Boy_Blue]

Hi
First:- Turn off the computer, press and hold the PWR button for 4 seconds.

Then - Leave only keyboard and mouse connected, disconnect all externally connected
devices such as Docking Station, USB storage devices, displays, and printers.
Unplug the AC adapter from the computer.

Next - Press and Hold the Power button for 15 seconds to Hard Reset.
Rinse and Repeat; Re-Connect the AC adapter.

NOW begin checking/testing/proving the Hardware is fit for purpose.
Power on your PC, press ESC (repeatedly), then F2 at the prompt.
Choose System Tests (Fast Test does a 4 minute hardware check).