Extreme II rampage memory problem

[simonis]

Hello can anyone help me please? i have Asus Rampage II Extreme X58 Triple DDR3-1800 9-9-9-24 CR2, but only two of memory slots working on the motherboard. first it was ok, all stols were working normaly, but after bios update one slot does not work at all.

 

[simonis]

system spec
CPU Type QuadCore Intel Core i7 940, 3000 MHz (20 x 150) (2.93)
Motherboard Name Asus Rampage II Extreme
memory Corsair tr3x6g1866c9d 6gb
Nvidia 295GTX (single)
hdd SCSI dell 76gb raid
OS Name Microsoft Windows 7 Professional (32bit)
BIOS Version 1802
power supply corsair 1000w
is it bios problem, or os? help me please.