Can't set custom white balance on my D7000
1> Hold the WB button down and rotate the rear command dial until the WB line of the top LCD is at PRE (bottom row, far right). You can set d1 to d3 with the front command dial.
2> Let the WB button go and half press the shutter release to return the top LCD to normal view. I do this step as a hold over from my D80 and it may not be strictly necessary with the D7000.
3> Press and hold the WB button until you get a blinking PRE in your top LCD. While it is blinking, shoot your white card or whatever you are using. If the camera was able to get a WB reading from the shot "Good" will be blinking in your top LCD. If it couldn't get a reading then "No Gd" will be blinking in the display. If No Gd, repeat steps 2 & 3.
Hope this helps.