I just got a box of parts from my brother - a rig I built him a few years back that died. I'm pretty sure it's the motherboard, but not 100%. Because the way it was acting, there is a slight chance it could be the CPU. The CPU is an i7-4790S, supports AVX2 for crunching, and looking at benchmarks, doesn't seem too shabby for 65W.

Since I have a PSU that tests good, GPU, SSD, RAM - if anyone has a Haswell / LGA 1150 motherboard just collecting dust, I could build another cruncher up. Another thought is if anyone has an older motherboard that would be willing to test this CPU, I could mail you the CPU and see if it's good before I purchase a motherboard for it.
Thanks!