Pc Won't Boot After Power Cut Off

I have updated my bios from f5 to f8k (latest version downloaded from gigabyte)the reason i have done this is because i want to upgrade my cpu to a phenom 2 955\965 and the latest version allows am3 cpusi have downloaded the latest version,upgraded the first time with @bios from windows (i know that was not wise but i didnt knew at that time)-restart--Computer didnt boot.Cleared cmos,entered bios -qflash- installed the old bios,everything back to normal.After that i tried upgrading to newest version with qflash.Upgrading went fine,restarted,loading factory settings in bios,rerstart,loading os,cpu-z showing the new verrsion of bios - f8k.the big PROBLEM is that every time i unplug the power cord from the psu,or just hit the on\off button on the back of the psu,the computer wont boot anymore.Fans come on,hard drive comes on and the cdrom is making a sound as the system would restart over and over again.IF i clear the cmos with the jumper,computer boots,everything is fine, but after power is cut it wont boot again until i reset cmos.I flashed bios again to the old version(f5) and the problem dissapeares.After that i tried flashing again,I tried every version but they all have the same problem.i teared the computer apart,checked everything inside,left only 1 stick of ram,video card and cpu cooler,still experiencing the same problem.what is the problem? i even wrote to gigabyte,they told me to:1) Turn off power.2) Remove the power cord from the PSU.3) Take out the battery gently and put it aside for about 5 minutes or longer. (Or you can use a metal object to connect the two pins in the battery holder to make them short-circuited.)4) Re-insert the battery to the battery holder.5) Connect power cord to PSU again and turn on power.6) Power on your system.7) If BIOS can POST, please enter the BIOS and load the fail-safe defaults setting.8) Save changes and reboot the system.I followed these steps exactly as they are written,no joy.I even brought the pc to an "expert" he couldnt help either,he told me i have bad luck.Thats a really bad joke!I really want to upgrade the proc and i dont want to buy a new mobo,i like this very much here are my system specs:phenom 9650 with zalman 9700 ntgigabyte 750a sli mobogigabyte gts 450 (planning to add a second one)2x 2gb kingmax 1066seagate barracuda 7200.12 - 1 tbarctic cooling fusion 550r - 500w,550 peakaerocool modern-v fan controller,3 fanswindows 7 ultimate 64 and windows xp 64 edition (i'm using it just for the horizontal span when i game,i have two 24" monitors)mobo and bios url...