[enri95]

When I was rendering for 10 min the computer froze with repeating audio...

I didn't have this problem when i had 4 gig ram?

 

[badatgames18]

what are the ram factory specs? and what are you currently running them at?

 

[enri95]

they are 1600 mhz v1.5 cl9
2x2gb
2x4gb

they are same kind of ram.

they run at 1333 mhz at default but i put 1600mhz...

 

[badatgames18]

if your at stock voltage with your 4.2 clock you might need to increase your vcore due to more ram.

When you have more ram slots populated you will generally need to increase your vcore as opposed to if you only have 2 slots populated... that is why

increase vcore above stock and see what voltage it is stable at..

 

[mymlan]

Run Memtest and see if your RAM is stable. Be sure to run as many Memtests as you have threads (i.e. 8 with hyperthreading).
http://hcidesign.com/memtest/

Edit: You might also want to try out LinX if you think it may be the IMC.
http://www.xtremesystems.org/forums/showthread.php?t=201670