Not enough power me thinks. The m2-atx is either 140 or 160 (if you have the HV not likely) watts depending on which model you have. 5amp at 12v is 60 watts. Now, just because the m2-atx is 140~ watts doesn't mean it pulls it all the time. My guess is it starts pulling it during bios as usually CPUS go to 100% usage during POST and browns out which is VERY bad for the MB.
I would definitely look for a bigger power supply. I'm thinking you need about 12amps at 12v to be safe for the 140 watt m2-atx.
I differ to oldspark whom will definitely respond to this and set you and me straight