I am new to all of this. I am doing a project that require 13 LED's, most of them are blue and hooked up to a 9v battery via parallel with each parallel a series of 2 LEDs. I have most of them hooked up but when I connect one single white LED all of the other blue LEDs turn off and only the single white LED is on. Now I don't think I am doing anything wrong, I am connecting it to the rig like the other LEDs.

 

What size resistors did you use?

http://forum.allaboutcircuits.com/showthread.php?t=69757

http://forum.allaboutcircuits.com/showthread.php?t=19075

 

I think it is because all your LEDs are in parallel.

Wire so that each LED has it's own series resistor from the 9V supply.

 

Can you post a drawing of what you have and how it's connected.
That'll make it easier to help

 

Apparently the white led hogs the current when you hook it up. Try a series resistor to limit the current.