This may or may not help.
Remove all of your old memory and just plug in the new memory and then test boot the computer.
Make sure the memory is in the correct slot.
On rare occassions you can get defective memory.
I ordered 1gb ddr PC2700 for my girlfriends computer. She has a gateway 310 and it says that it is compatiable with pc2700 and it can support up to 2gb of ram but when I installed it in the computer it would act like it was going to boot up into windows but it didnt. It just reboots itself right before the Windows XP boot up screen over and over. Whats wrong?thanks