Why does my PC freeze after installing new Ram?

DeeSull

Hello, i recently added 8gb of ram to my existing 3gb of ram to make it 11gb of ram. But after doing so i noticed i would get random computer freezes to the point where i had to force it off my pressing the power button as Alt Tabbing and Crtl, Alt, Delete would not work, particularly while playing games. My original ram of 3gb was a Kingston 1gb stick and a 2gb stick both running at 1333mhz in duel channel (unsure if these will work in duel channel as they are both different sizes). I added 2x4gb Samsung ram also running at 1333mhz in duel channel. My motherboard is only capable of duel channel and has 4 slots and a capacity of 16gb. I removed my original 3gb ram and just went with the 2x4gb and since then i have had no freezes. I was just wondering why this was happening? 

Any advice would be appreciated, thanks.

My PC specs are:

Acer Aspire M3910 M5910 DX4840 H57H-AM2 Motherboard. 
4x8gb DDR3 1333mhz Ram.
AMD HD 7770 1GB GPU.
Intel i3 550 CPU.
600GB WD Blue HDD 5400RPM.
240GB Kingston SSD.
300w power supply.

billsey

When you put in a pair of 4GB modules it switched to dual channel mode. In dual channel mode you need each pair of modules matched. That means the 1GB and 2GB modules aren't working. They need to either be a pair of 1GB modules or a pair of 2GB modules. I'd be real tempted to swap them out for another pair of 4GB modules to max your system at 16GB total. Before the 4GB modules went in you were in single channel mode...