Extensa 4630z will not boot after centon ram upgrade

I have an acer extensa 4630z laptop. Originally it has 2GB of DDR2 667 Mhz memory. I replaced them by 2 2GB DDR2 667 soDIMM modules from centon. This is what the laptop specification says to do, if you want to upgrade to 4GB of memory. The laptop won't boot after that. When I pushed the power button, the power went on, but the computer did not boot. The screen was just black and there was no error information, etc. I am about to try to return the memory to frys if they will take it back. Please help, thanks.