Thank you, ***** ***** understand what you meant about the black cylinder.
Ok, are we certain this isnt a monitor issue? Lets completely disconnect and reconnect the monitor.
Also, since you say the back lights up. lets try a pram reset
Shut down your Mac.
Locate the following keys on the keyboard: Command (⌘), Option, P, and R.
Turn on your Mac.
Press and hold the Command-Option-P-R keys immediately after you hear the startup sound.
Hold these keys until the computer restarts and you hear the startup sound for a second time.
Release the keys.
Now, will the mac turn on?
If not, when you try to turn it on if you hit the caps lock key, does it light up?
If yes, stop here and let me know. if the caps lock key doesnt light up, continue.
lets try removing and reseating your memory as follows https://support.apple.com/en-us/HT205044
Please thoroughly try each step, respond to each question Ive asked, and dont skip anything!