A lot of online sources point to motherboard so it's time to buckle up and go through a nightmarish RMA.
If you bought it from Newegg, it won't be nightmarish at all. It can all be done online, even the shipping label if you want. They will send an email saying the RMA has been approved, and all you do is package it up and drop it off at UPS, USPS, or your favorite shipper. Unfortunately it takes about a 3 week turn around to get the new one.
What I usually do, is order a new board before I RMA the old one. Then tell them to 'refund' rather than replace, but no re-stocking fee because you are buying a replacement to expedite the PC assembly.