12gb ram shows in bios, only 4,6,or 8 usable shows in windows

Hi guys. I just upgraded my processor to an AMD 8350. It replaced my Phenom. This is the 3rd day the new processor has been in the computer. First two days everything went fine. Ran Prime 95 and IBT to make sure i was up and stable. This morning (3rd day) got up, turned on the computer, and now i have less usable ram than i had last night. No matter how many times i restart, it shows less in windows than what bios shows. It says either 4,6, or 8gb usable ram (it changed just about every time too). I have reseated all the ram. I have moved them around. I have reseated the processor. I have clean installed windows 7 home premium x64. Does anyone have any ideas? This is the first issue with RAM i have ever ran into. Also, when i am in bios, and i go to the RAM settings, everything shows up like it is supposed to. Details, options, timings, etc. Not really sure where to go from here.

Thanks for response. Voltage is correct for RAM. RAM is all crucial. 2 4x2 and 2 2x2. Same speed. 1600 mhz. Same clocks. I am gonna try putting phenom back in. That is good idea. Maybe 8350 is malfunctioning. All I know is everything was fine til third day after installation of new processor. Then half usable RAM issue popped up. And the processor is all that was changed. Btw, no oc. Thanks again for ideas.

It appears that one of the sticks of RAM died, as the computer would only boot with three of the four. Soooo, gonna send it back and get a replacement. Pre labeled package on the way. thanks for the help. Btw, i did put the phenom back in, and it still didn't do the trick, that is why i started the RAM switching. thanks for the help mellon head.