This unfortunately sounds like a hardware defect (CPU or motherboard).
Is the co-worker you bought the motherboard from a “dick”?
Otherwise you can ask if
- You could borrow a CPU from him (if it fixes the issues RMA your CPU)
- He/she/it could do an ASUS RMA with the motherboard, IF ASUS only does warranty service for the original buyer.
I have bricked my ASUS Pro WS X570-ACE with a BIOS setting permanently and already contacted ASUS support.
There you just type in the SN of the motherboard to create a ticket, I guess since the motherboard cannot be older than the warranty period they don’t ask for an invoice from the original buyer.