Its hard to say what caused the problem so you will have to use the process of elimination. I would start with the PSU. You will need a volt meter to check the voltages for the mobo cable to ensure that they are in line with the PSU specs. If not then you need to contact the PSU manufacturer to see what recourse you may have. If the voltages are good then it could either have been an internal mobo short or something caused by the case. Hopefully it was an internal mobo short so that you can RMA the board. I know you are really frustrated so hang in there.