Q: SOS, iMac freeze on grey screen after a hard fall! (pics)

I have just made a huge mistake, I drop my iMac (2014-2015) retina to the floor and broke the screen. I tried to turn it on after that but it is stuck on a grey screen (no apple logo) after the startup sound.

It was plugged and working when it falls, but a second before reaching the floor it unplugged.

I can't afford to not fix my iMac and throw it away.  I know I need to buy the screen, but what else can be damaged? how to test if the hard drive or other component is dead? please help me if you have any idea what can be wrong with this.

Thanks in advance, Giovanni.