I'm having the same issue. I can get my build to boot once every so many tries directly to the BIOS. The best I've come up with is that setting the PCI-e slot to Gen1 (which is NOT ok with me). I'm shopping around for a better riser currently
Here is my work in progress. I had it all together only to find out that my riser cable is defective
I plan to change it over to hard tubing someday, but I just used what I had leftover from my Urban 81 build.