|Something like this happened to me a few years ago..|
Have you cleaned the inside of your PC? Specifically, have u checked to see the amount of dust/dirt that has accumulated on and in and under the CPU?
If you haven't cleaned out the inside of your PC, do it now and try again.
If the above is not the case, then perhaps it is your motherboard. Clean out the memory slots on the motherboard and try it again. If that doesn't work, then try your memory on a friends computer.
If your memory works perfectly on your friends comp, then it's your motherboard.