Can't Use External Mic?

Whenever I try to use an external mic on my computer (headset, stand, etc.), the mic doesn't pick up any sound but the internal mic does instead. Like say if I were to record something with the external mic, the sound picked up would be exactly the same as if I unplugged the external and just used the internal. If I mute the internal mic the external still does not work and will pick up no sound. Whenever I try to configure and set up the external mic, it will claim to hear nothing whether or not the internal mic picks up sound. I've tried several solutions but nothing seems to work. If it helps; Dell Windows 7 Home Premium with Intel Core i3 CPU Processor 3.80 out of 4.00 GB usable I've checked; the external mic is NOT muted and my sound card driver should be up to date