ASUS P4800 SE problem with enabling performance mode

[Dbiss]

hi all, i just fininshed installing my P4 and i'm having a small problem with my ram. I got 2 x 256 of OCZ dual PC 4000 gold EL ver 2 and i can't enable the performance mode it show in CPUZ that there are dual mode but performance diseable. I follow the instruction and there are in the right location dimm 1 and 3. I look in the bios and set the ram 400.
Any help would be appreciate.

thanks

Asus P4P800 SE P4 CPU 3.00GHz @ 3.7 GeForce 6800 GT Leadtek WinFast A400
2 x250 OCZ PC 4000EL Gold rev 2,PIONEER DVD-RW DVR-108,2 x120g seagate Raid 0, LITE-ON COMBO LTC-48161H xaver III, Antec True Blue 480