Internal hard drives disappear and won't return, but are visible in an external usb enclosure

[Hammey]

Hi well just to cover one problem Ram is never to be mixed with other brands or even the same brand and part number. If you want 16 gig Ram it should be 2 sticks of 8 gig each that come in a 16 gig kit or you will have problems I am surprised it does not start or reboot all the time with the Ram you have. Next what 750 power supply is it Make,Model how many 12 volt rails and what are the amps on the rails. Is the system Bios up to date on the new motherboard. Just looking at your Ram setup I do not see how you could have it running properly in Dual Channel mode and all those modules wont equal up to a dual channel function. So when you look at it there could be a few configuation problems causeing the errors.