Why isn't my microphone working?

i'm using an xbox headset with an adaptor so that it will fit into my computer. the computer doesn't have a built-in microphone. when i try to check to see if its working on online testers or testing it with programs on the computer, it tells me noise is being made but not relevant to when i speak or blow in to the mic, ie when i'm silent sometimes the noise bar will go high and when i talk it could be very low. everything points to the microphone working, my computer is picking up a microphone, it's just not. what can i do to fix it?