Their can be 2 things wrong in my experience of this, 1) Your Memory Controller on the CPU is damaged, or 2) you have bent CPU pins and the mem Controller ones are not making contact(or CPU is not seated correctly).
Have had this issue with the 1366 sockets and the 1155 sockets.
And the "Yeah but it worked for 6 months and suddenly", doesn't apply here, are you using 1.65v or 1.5v Ram?
1.65v can damage you RAM controller on your CPU over the long run, you can google this with poeple having their Boards and CPU's die after a couple of months of using 1.65v ram.
Just check, you can also test it by only inserting 1 or 2 sticks, and then seeing what happens if you still have a large number reserved.
on a side note, I also contacted Corsair and they say that they can only recommend multiple sticks working together if you buy them in kits.