Can't get memory sticks to work together

I think you can be assured that if your system doesn't boot up with one stick of RAM in particular, and it works with another (in all slots), then that stick is the issue. Exchange it for a new one, RMA it, or just get new RAM. All motherboards will POST an "overclocking failed" message if the RAM fails, since it could alternatively be caused by too high of a memory overclock (it can't tell the difference, to the motherboard, the memory is just not working as it should be).

Just to be sure, I would boot it up with the other stick and run Memtest86+. It's always a good idea to check the remaining module to see if it has any (undetected) errors as well, and you should do this with any new RAM you place in your system (even if it's brand new).