I just recently bought a new pc with the following specs:
AMD Athlon 64 X2 3800+, Gigabyte GA-K8NF9 Ultra, Corsair TwinX PC3200LL XMS 2x512MB @ 2-3-3-6, EVGA Geforce 7900GT CO SO, 3 Harddrives (total of 580gb).
I tried overclocking from bios, I changed HTT/DDR ratio to 2/1.83 (if i remember right) so when HTT is 231mhz the DDR would be 210mhz, HTT multi to 3x and cpu multi at 10x. Just after I save bios and restart I see this msg infront of me when booting: "Over CPU Clock Right Now! CPU Clock Frequency 231Mhz" after this msg it boots again, and says "Skip, CPU Clock Frequency 231Mhz". I'm asking myself whats that about?
I went in windows xp and opened CPU-Z, and indeed the HTT freq didnt change, but the other options did, the memory ratio and so on, so I opened EasyTuner(gigabyte overclocking supplied program) and overclocked the Fsb with no problems at all even up to 240mhz (and memory at 220mhz) and having the cpu running at 2400mhz at 29c idle.
Its obviously not an overclocking problem, but some option I'm guessing in bios to skip this OC, if anyone knows a solution for this I'd really appriciate it, Its annoying to overclock my cpu everytime I go into windows. Oh and I get this Skip overclock msg even if I overclock the HTT to 205Mhz from 200 after booting.
Sorry, I can't offer much help here since I've had the same problems with a X2 3800+ and a GA-K8N ProSLI. No matter what I did I couldn't get a decent, stable BIOS overclock out of it.
I'm stuck with EasyTune for now but, surprisingly, it works fine for me, as I can live without a constant overclock.
I had tried previous versions of EasyTune and the amount of memory they needed made the overclock useless, but the latest version is pretty good.
Example: X23800+@2400MHz (+20%) reduces render times in 3dstudio by 18% from the stock 2000MHz.
In any case, if someone knows better and has found a solution i'd be glad to hear.
 By the way, with EasyTune I found a ceiling at 240FSB even though my memory is rated ddr500 regardless of voltages and dividers used. 240FSB OK , >240FSB Crash
Ah thanks for the reply, now I know I'm not the only one, and btw I cant seem to get my fsb higher then 240FSB with EasyTuner as well. 240FSB - just fine, anything above - crash(with divider on memory and so on).
I had same probs as you when it came to overclocking....easy tune would work but i couldn`t get the bios MIB tweaker over 215mhzfsb....anyway after a few e-mails to gigabyte they have sent me a new revision C of bios version F6... i can now overclock to 2.6 STABLE...but i think 2.4 is good enuff-don`t forget to change the hypertransport multiplier and memory dividers accordingly-i have corsair mem..ddr 400.
P.S Easy TUne is **** cos u can`t change mem divider or H.T multiplier
Anyway if u want the bios update let me know and i will e-mail it to ya
I did tell Gigabyte that i had seen a lot of other people having the same trouble in forums and they said they are going to release official update but did not say when.
My MB is slightly different than yours. It is a K8NF-9 and I had a bit of trouble overclocking it. The final solution was to drop the multiplyer back to 9.5 and then raise the clock rate to 275 Mhz with a bit of extra voltage as well and also adjusting the RAM timeing to keep it all happy.
That worked extremely well however leaving the multiplyer at 10 or dropping it to 9 just would not work. I cant figure it out but very happy now.
The F7B (2008/10/22) bios is available here http://download.gigabyte.asia/FileList/BIOS/motherboard_bios_ga-k8nf9ultra_f7b.exe and does indeed fix the issue. Only thing is that keeps defaulting to 'Auto-detection' for the IDE devices so for me I just set each back to 'none'; A bit annoying but nothing compared to the benefits of this bios for overclocking! Without to much bother i can push my X2 3800+ to around 2700mhz. Forget i7's