well basically to get the card to work at 4x - u need to do what u did
change the option in the bios and save changes when u exit the bios
have a 4x card - install the cards latest drivers - install direct x9 - install motherboard chip set drivers -
is there a bios update for your gfx card or bios available that u dont have?
do u have a buddy with a 4x enabled mobo u could ask to try the card to see if it actually does go to 4x