Both sticks must be the same make and model or you see issues like that. I stick with Crucial for such upgrades. Did you?
I have a ASUS X-75A laptop and it only had 4gb of ram so i did the research and baught a 4gb stick DDR3L-1600 SODIMM. The laptop see's it and say's now i have 8gb of ram, but it seems slower now and after awhile it locks up. And i have to do a hard restart to get it work start working again.And it never did this before.