Check the voltage requirements of the new memory. If it requires more than 1.8 volts, you may have to reinstall your old memory, up the voltage in the BIOS using the manual option for the memory voltage control to the voltage required of the new memory, shut down, and then install the new memory.
Try resetting the BIOS.
You can also try with only 1 stick to see if you can get it to post, and go from there.