Check your risers they be burned.
are you sure that "burned raiser" is not an urban legend?
bad molex contacts is something I encounter very often, but actually burned raiser is something that I haven't seen yet, but then maybe I'm just that good

"If you're not failing, you're not trying hard enough."
Here is a pic of one of my failed risers, I usually caught them before they went this far, but this is an extreme example.
