Are they in the right slots? On my Shuttle motherboard which has dual channel capability & 4 slots, I have 2 sticks in slots 1 and 3. I.e. in different channels. (The next two I buy will go in 2 and 4.) If I had put them in slots 1 & 2 dual channel would have been disabled.
So do you have 2 sticks of identical memory, not both installed on the same channel?