After you replaced the Mobo and CPU did you reinstall Windows? If you didnt that will be where your problem is. You have different drivers than you have hardware.
Was this a i5 or i7 system? You needed to increase the CPU VTT voltage or it may be called the QPI/DRAM Voltage. It's actually a fairly common issue with system that have 12GB of memory or systems running High-Speed Modules. I wish I had noticed this thread sooner, sorry.