Monitor remains black

Good evening!

I've been dealing with an issue with my desktop for a couple of days, and it's literally driving me crazy. So, I'm seeking this place as a final solution. I hope someone would be able to be my savior!

The issue is: My LG monitor goes black once I turn my computer on. I know, it's common. I've tried so many solutions but nothing worked. So … let me list them now..

I checked the cables. All of them. It's not a cable issue.
I connected my monitor to another laptop, it worked perfectly fine.
I tried another graphic card. Nothing happened.
I cleared my CMOS by removing the battery and placing it back, still nothing.
I really lost count of each single thing I tried, my screen is still blank and it only shows "Power saving mode" for few seconds once the computer starts working, then mere blackness.

There's a thing that might help in figuring out the issue, my keyboard freezes once the computer starts. I tried to press Numlocks but it doesn't respond. I know I'm unable to see a thing, but all three lights on my keyboard flicker once the computer is on then they shut and never respond again.
I thought it might be a weak power supply thing, so I disconnected my RAM, Modem, Audio, USB, all of my drivers . I kept my only the main parts and tried again. Still nothing.

I cleaned all of the slots, fans, and the whole case. And it's the same.

I spent like two days trying this and that. An hour ago I gave up. Connected everything back, all the screws too, secured the pieces in then closed the case and started it. It worked but it froze on the black 'Award' screen with a BIOS error message and "Press F1 to continue. Press 'del' to enter BIOS"

I guess that message is because I cleared my CMOS or something. But in case it's related I had to list it too. I tried to log into the BIOS menu by pressing "Del", the keyboard didn't respond. (back to the freezing thing I said earlier).
I tried to restart it, and the black screen welcomed me again… C:

I'm really lost and tired. I know I've written too much but I just didn't want to read same solutions again. So please please please help me….

Thank you in advance~
Yunie <3