How to fix my Macbook Air A2179

To [try] and make this as short as possible.

I purchased an Apple Macbook Air from someone.

The seller did not tell me it was not restored to factory settings AND that he didn't know the password. I was furious!

I'm slightly tech savvy. So I tried following someone's instructions online to restore the computer. After that, the mac came on as if it were a new computer. Until it got to the point of asking for a firmware password... Of course I didn't know it..

That night I did not leave the mac plugged in. So it died. The next morning I tried to turn it on, and nothing. Absolutely nothing. The screen stays black.

Now I've LITERALLY tried just about 30 or 40 different ways to fix this, and nothing has worked so far, but I am willing to try more things to fix this issue. I mean I'm already out so much money, I'd prefer to figure this out on my own.

The last thing I tried was taking the back cover off, after having left it on the charger for 5-7 hours, and after taking the cover off, I found the power wire and pulled it out for a while, then hooked it back. This still did not work.

PLEASE GUYS, ANY SUGGESTIONS WILL BE GREATLY APPRECIATED!!!!!

Thank you,

Kellz19XX