Are you dealing with a laptop or a desktop? If a laptop or a prebuilt desktop, we'll need an SKU. If it's a system built with off teh shelf parts, then please list the specs liek so:
In the mean time, can you parse the make and model of both sticks of ram? Often times there are minor things we can overlook that can cause us to pull our hair out. Are you on the latest BIOS update for your system?