ihave 2 x4 already vengeance corsair ddr3.1600


need 16gb total

ddr3 is dead
dont waste your dosh
get new setup

If you want to upgrade....

I've never had this issue but sometimes if you buy 2 more sticks to add in to the existing, crap can hit the fan. If you can return, then try 2x4, if it doesn't work, return and get 2x8.

Also, I never had this issue because I just replace all the old ram.