I got a Lenovo ThinkPad L440, and it turns on, but no screen, no booting. It does however beeps, not the five short ones, but the “five short-pause-five more short-pause” way, which (supposedly) indicates a different error than motherboard error. Allegedly it was “set aside and not used”, and when taken out yet again years later, it didn’t work. It does produce a different beep code if the memory is not present (don’t remember the exact one), and also produced a long beep until I replaced the CMOS battery right after the “regular” ones it did.

I have reseated the eDP cable to see if that was the issue, but it seems that’s not the case. I’ll take it even further apart, to check the capacitors if they died, also the display power cable if there’s any (could not find it under the keyboard).