12gb ram +

[meanman]

My mobo is a gigabyte EX58-UDP4 Intel X58 and i have 12 gb of ram i installed the ram and it recognised 10gb of it. i did a bios update and it recognized all 12gb although in windows (win 7 64 bit) it said 12gb (11,5gb usable) i was happy then i noticed the I7 920 was running at 2ghz so i went into bios and changed a few thing and the cpu is now running at 2.67ghz but the bios and windows now only see 10gb of ram.
Any advice would be helpfull.
i am running the latest bios .

 

[linkin]

You got the MAXMEM option in msconfig checked? If you do, uncheck it, apply and reboot. If you don't have it, try setting up your RAM speed, voltage and timings manually, see if you can disable any memory caching/shadowing options in the BIOS too (looka round in chipset options/settings)