When you say it won't boot, does it not post and/or does Windows fail to load?
Just to be certain it's the board, do you have another graphic card to test in the first slot?
Also, if you haven't already, use a can of compressed air to blow out any dust or particles that may be in the slot.
Intel i9 10850K@ 5.3GHz
ASUS ROG Strix Z490-E
Corsair H115i Pro XT
G.Skill TridentZ@ 3600MHz CL14 2x16GB
EVGA RTX 3090 Ti FWT3 Ultra
OS: WD Black SN850 1TB NVMe M.2
Storage: WD Blue SN550 2TB NVMe M.2
EVGA SuperNova 1200 P2
ASUS ROG Strix Helios GX601