In my case, it was a video card with a defect and the PSU was OK
Last year I tried loading a 7900XT Hellhound into this system and the same behaviors started except NO hardware detection.
Lights on, beeps 1L3S at post with VGA lamp stuck on, no picture, no fan spin. Card presumed dead,
every helpdesk stuck on stupid.
It's an unfamiliar behavior and I've only gotten it before with my RX580 when the power connector was unplugged.
Antique power supplies run ALL my equipment. The rack runs a custom loaded Cooler Master 460W and this box an Antec EA-750.
These are all sub-25A power boxes and they won't run newer cards. It took months to figure out because this information is hidden.
1L3S isn't the failure code. So I don't know what to do with that information and they seem related but I can't connect those dots.
When I put the bequiet! pure power 12 M to use, it will be specifically to deal with this problem.
Making the jump to a high watt PSU is not the answer. You have to pay attention to power draw.