2002 Isuzu NPR pipe box truck?????

I have a 2002 Isuzu. It has a problem with the headlight and signal light. I have already changed the switch for the headlight but it still does not work. The weird part is that the wires have power going to the headlight but there's no light coming out? I checked all the fuses in the front and they all seemed okay. Any suggestions on what can cause this problem? Can you please help me find a website or any other links where I can order the part I need to fix this problem or any store that can have this part. The light is not burned out. The truck info is : 2002 Isuzu NPR pipe box truck EFI. Hope that helps. Best answer gets five stars. Thank you.