i literally just had the same exact problem you are having and found almost nothing about it anywhere online!
so because i KNOW how insane this is driving you, and because i know that youve prolly tried just about Everything, im in the process of exchanging out my mobo for a identical mobo. that way at least ill know if i am honestly a moron or if its the board
mine was a BIOSTAR mobo with an AMD 2200+ combo from compgeek.com
ill keep ya posted!