I purchased two Dell 1G memory sticks to add to the original two 512 sticks in my Dell Dimension 8400 desktop.  The 512's are in slots one and three, the 1G's were added to slots two and four.  The computer will not boot with the added memory and the following message appears on the black screen:  " }300 SE 128MB BIOS P/N 113-A33406-100"  When I remove the 1G sticks the computer boots normally but a message appears saying new memory has been added and press F1 or F2 to either boot normally or change the configuration.  I also tried adding the 1G sticks in slots one and three and got the series of beeps referred to in the installation instructions for the memory sticks that indicates the memory is not being recognized.  The new 1G memory is the recommended memory from the Dell website for my computer and is Dell memory, however it is 666 speed vs 400 speed (I believe) of the original 512 sticks.  Any help getting the computer to recognize the added memory will be appreciated.