The following quote is from Kingston Technologies web-site.
* Check your owner's manual and compare the specifications of the memory with the specifications supported by your motherboard manufacturer.
* Check that the module has been seated completely.
* Install the largest capacity memory module first.
# For most installations, DDR modules can be installed in any available expansion slot. Other installations may require the memory to be installed in a particular sequence based on the modules capacity. Check your owner's manual to determine the correct installation sequence for your configuration.