HELP NEEDED!! new ram installation:help:

[kainthebigboss]

Hello,

I bought a new ram for my laptop and when I install them as dual the laptop just don't start the windows and keep giving me black screen, and when I try to enter the setup screen it works and it shows me that the ram is recognized!!

my laptop is TOSHIBA P100-222

the ram I bought are 2 slots of (Kingston 2GB DDR2-667 2 GB G SODIMM Laptop SDRam) that its total of 4GB

my laptop support up to 4GB ram so I don't think that this is the problem, it was running 1GB ram as (2 x 512MB) dual but when I install it as (2 x 2GB) it doesn't start the windows !!!

now its running as 2.5GB as ( 512MB + 2GB ) and I tried both of the new rams as alone on it and it dose start so the ram slots work as singles but looks they don't love each others

any ideas about what is the problem here

thanks in advance