Hello! I have purchased Dell Vostro 15 3515 laptop 6 months ago! The laptop camed with 8GB RAM memory. Now i want to upgrade to 16 GB but when another 8GB RAM stick is put in the second module the laptop doesn't boot - the keyboard lights up and the power led indicator flashes in both white and yellow but the screen ramains black. The service tried with couple of RAM sticks from different brands including the same RAM stick as the original - i mean exactly the same in all specifications! Can you tell the reason why i can not use both RAM modules in the same time? The original RAM memory is Hynix 1Rx16 PC4-3200mHz. Also the problem is not in either the sticks or the modules - all of this was checked and they work fine separately.