3 beeps, does not start

I've had this laptop for a very long time, I replaced the logic board, screen, keyboard, fixed the light...

Everything was working just amazing before the "El capitan" update, then my computer took a huge dump.

I could not use my keyboard nor the mouse to even log in, it would not work... not even a connected mouse. I went to apple, they couldn't figure it out. Then I took it to another place and they could not find the problem, but this time, now I can't even turn it on. It beeps 3 times... so I decided to do it myself, got the 1 TB SSD, replaced that, found a missing ram, replaced it with the 4GB and changed the disc slot for a secondary SSD (empty).

Upon opening the top, I found that the bluetooth box was corroded, and there was white corrosion all over that side where the hard drive sits. (Can that cause beeping?) There's no way my logic board is fried after spending 1000 dollars on a new one... I've read that the El capitan update basically reconfigured the board... is this true? If not can it be fixed?

Any advice would help. I've pretty much replaced almost every part, so I don't even know what to do anymore... I refuse to give up on this baby.