As the subject states, I'm working on a custom backplane motherboard, similar to those that you can purchase on Aliexpress for 165+ dollars that has 7 ISA slots and 1 PC104 slot. I've included some features I've seen on other similar projects such as an option ROM socket and CPU activity circuit. My first version worked pretty well after some bodge wires required due to some silly mistakes on my part, but it used at 555 timer to make the standby LED pulsate. I didn't love this feature since I don't really need it to do that so in my second version, I THOUGHT I would remove that option completely and just have +5VSB feed into a 2N2222 transistor and power the LED when the +5V rail has no power and turn it off when the ATX power supply is turned on. the problem is, when I did this and spun a new batch of boards, the LED did not work properly. for some reason, it comes on when the ATX power supply is off but stays on even when the supply is turned on. I checked the schematic several times and even had ChatGPT check it for me. I built some test circuits on a breadboard and have the same problem even though it SHOULD work as long as the transistor is biased correctly.

Long story short, does anyone have a suggestion for a WORKING circuit that can do this with as few components required as possible?
If I have to, I'll go back to the 555 timer but I'd hate to continue using a component that doesn't actually do anything of value.

Also, if this should be posted somewhere else let me know!