6 GB of ram installed but only detect 4 GB.HELP !!

since this board work with 3 channel memory did you put the stick in a1-b1-c1 slot and write in the user manual http://dlcdnet.asus.com/pub/ASUS/mb/LGA1366/Sabertooth_...

Do you have three 2 GB sticks?

@scout_03 yes,but my pc doesnt detect b1 ram slot  

Yes its 3 x 2 gb each

Yes thats the order i put em.but i dunno why b1 doesnt be recognized by my system.It only says Ram Slot 1 and Ram Slot 3

bump  

Try removing all 3 sticks and then install just one stick in B1. If it doesn't show it as 2GB, try doing the same with each of the other two sticks. If each doesn't register as 2GB, you have a faulty B1 slot. If two sticks register 2GB each and the third doesn't, you have a bad stick of RAM

And then how i suppose to fix it ?

if it is the board or the ram the same would be rma for the defective part

A Scout 03 stated, if the MB or RAM is defective, you will have to return it for a replacement.

Try running memtest86 to test the ram, if all the ram modules pass this test then I assume its the mobo with the problem as cmichael138 says you may have to replace the mobo or ram. I had the same problem and its a right pain.