Hey!
I've got an Asus X555LD with 4GB built in ram too. I have had the same problem guys, tried to upgrade with 4GB more ram. I bougth an 1600 MHz, DDR3 ram. Turned out, that the built in ram operates on 1,35 V, and the ram i wanted to use was 1,5 V. Today a bought an 1600 Mhz, DDR3L ram, which...