MacBook wont start, fans and white light on front turn on for a bit

I just got a Macbook pro 2012, used it for about 5 hours and now doesn’t boot, the front white light turns on and abruptly turns off. Same with fan. No screen info, no chime, even battery charged to 100% (tried without battery). I tried the resets as well, multiple plugs, and nothing.

before the unexplained death, the K and L keys didn’t work, neither did the ethernet port, the power button worked well, the HDD was changed for an SSD and that’s it.

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What does the onboard battery checker tell you? All 10 LED's lit, do they blink or stay on?

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