Doesn't look like it's been mentioned in this thread, but make sure you have the RAM in the right slots as per the manual for the motherboard.
It looks like you've swapped boards and RAM throughout this thread, so I'm not sure which to lookup for you. Most AMD boards need slots 2 and 4 occupied (assuming dual channel setup). A lot of us are accustomed to it simply not mattering on Intel, but on AMD it makes a world of difference.
A picture of the PC in it's current state could help too. Pictures say a thousand words