Suddenly 2 rams not working

[adi576]

I have 4gb and a 2gb stick they were working fine until now ,
Suddenly my pc won't boot,
I opened it up and tried cleaning rams and both of rams are fine when booting with single stick ,
both mobo slots are working as well but only with single stick ,
They just won't boot together ,
I've tried different stick 2 sticks just won't boot...

 

[wesleyh2003]

RAM can eventually fail and because one stick is working and one is not you know which one needs to be replaced.

 

[smorizio]

run memtest from usb stick on each stick. also post your hardware info here.