1. Make sure the RAM notch maches the slot indentation before pressing the RAM module into the slot.
2. Press both RAM sides at the same time but press one side harder till the plastic latch snaps into place, then do the other module side.
3. Make sure RAM modules snap/click into place
4. Only check you have to do from Windows is to verify that every RAM MB is being recognized and usable.
Open Control Panel > System and verify the Installed RAM size number corresponds with the total installed RAM, meaning it's all recognized and usable and all is good... and in case you see two figures, one for Installed RAM and another for Usable RAM size, you have a recognition problem.