3 beeps but is not ram

Hi everyone i’ve an issue with the late 2012 Imac, at first it was beeping three times so i thinked about a ram problem, but after replace it (and ssd), mac continuous beeping. This issue not happen every time i boot it up and sometimes i’ve been able to work for a lot of hours without the problem happened.

So when it was happen (before to defenely close it after updated ram and ssd) i’ve look at the fours leds on the motherboard and the last two (gpu and lcd leds) was off.

PS. I notice (but i need to verify this) that if i tilit it up the problem happen with less frequencies.

I’m sorry for my bad english, if i’ve wrote down something unclearly please notice me.