Hi CostabelBr,
I had a similar issue a few months back with an 8GB (2x4GB) kit of Corsair Dominator 1866MHz.When the 2 sticks were in the Motherboard the Bios would sometimes (not always) report that 8GB was installed, but only 4GB was enabled, it was the same in Windows too, it would show 8GB installed but just under 4GB was available, and it didn't matter which sticks the Dimm's were in.
However, just like your problem each individual stick worked fine on its own! I only every got the problem when the pair were together. (Like 2 good mates that only ever get in to trouble when they are together, whos to blame?) So I could never pinpoint which module was at fault. The only way I knew it was the memory causing the problems was because I had another 8GB (2X4GB) set of 1866Mhz memory in another PC that I could test.
I got in touch with Corsair and told them the story and they agreed an RMA, the brand new replacement I received work fine. The only downside to RMAing to Corsair from the UK is I had to sent them to Holland at my cost.
Anyway, the only way you are going to tell if your Sticks are faulty is by trying the sticks in another PC, or trying other sticks in your PC.
As for compatibility issues, a good stick of memory designed to work in a particular interface should work in any of the mainstream motherboards.
If you have a receipt return them to whom you bought them off and get them replaced, Corsair mem has a lifetime warranty.
If you've lost your receipt get in touch with Corsair support, they rarely ask for an invoice, but reserve the right to do so.
Tommy.
