What make/model is the PC so we can try and see what the led code means, I assume it flashes?
Possibly need these - https://www.computerhope.com/beep.htm
if its AMI Bios, 1 long & 2 short = Video card memory
Award - Also video card error
IBM BIOS - Video card error
looks like a pattern there.
fact screen works until you hit enter is interesting one.
possible the light signals are BIOS codes, but then what are they?