Please Help! Inspiron 1545 Microphone/Speakers constant buzzing, no audio!

I have a Inspiron 1545 and have only recently realised there is an integrated microphone in the laptop! Previously when using Skype to make webcalls, I've used an external microphone as I couldn't work the internal microphone and eventually assumed there wasn't one. But now I have been trying to make the internal mic work as I've looked on the forums to find I should have one. I went on the Dell Web Cam central,  IDT Control Panel and Sound control panel to try and alter the settings, but now all I have is a constant buzz coming from the speakers and I can't hear anything else, even when I try and play music! I don't know what I've done, please help!