What do you mean with the system sees only half of it...is that Windows or is it the indication during the boot phase?
Enter the BIOS, how much do you see there, exit the BIOS with the SAVE and EXIT function, any changes???
By the way, as far as I know, you need to enable the second slot as it is not active as standard option, maybe some interference has caused somehow to alter the setup....consult the manual.