Dell G15 5535 - Opens to Dell logo then goes completely black.

So I opened up my laptop a few days ago to replace the keyboard, and everything seemed fine until I tried to turn it on again. It opened to the Dell logo, and loaded for a moment, before the screen went completely black. The backlighting on the keyboard was still on, so the power was still on, but the screen just wasn't showing anything - didn't even get to load Windows. I've spent the last few days trying various fixes. 

- Gave it a power cycle - same result

- Ran diagnostics - no issues found

- Loaded it with a second screen attached - the screen turns on, but goes into power-saving mode as soon as the screen turns black

- Tried loading into Windows Autorecovery - won't load at all

- Reset the Bios settings to default - same result

- Can't load in safe mode

- Tried to cleanly install Windows using a USB - I can open into the USB via bios, but it just does the same thing: loads the Dell logo then goes completely black

- Tried to flash update the bios - First it wouldn't allow me to press Y to confirm the update, and now it's barely flashing the confirmation screen before it goes black.

Does anyone have any other ideas before I just resort to buying a new computer?