Well, I don't want you to give up!
Go into the nvidia control panel. Make sure if you have AA on there at least turn it to multi sampling. Or turn AA off altogether.
Otherwise put all global changes to the minimum - no AA, no AF etc etc.....
Then run 3dmark and see what you get.
If you still cannot reach 13K marks, go here and follow the instructions
http://support.microsoft.com/kb/310353
Then run the benchmark, check your score.
(It might as well be that you turned your settings up for better graphics in some game, and then those same game settings which you turned globally would be directly affecting your 3dmark06 score).