I bought 2x4gb of ram one month ago. When inserting them and booting my pc it tells me 8gb detected and 4 usable. This is if I put them in dual channel. If in single channel, it works perfectly (8 usable). I tried both channels, and every possible combination. It seems the two top slots are not working even with a single ram inserted.
I changed my motherboard and im still having the same problem. Tried ram at my friends pc and it worked fine. Im wondering if it has something to do with my cpu (No broken pin though).