Check the volume control of your operating system. ie ... 'Volume Control' located in the 'Progams - Accessaries - Entertainment' menu if you have a Microsoft OS. There should be seperate property settings for Recording and Play back. Make sure 'Line In' is not muted and that the level is up. The mic jack is a low voltage (a few millivolts)/low impedance input. You might get a fairly good signal if you plug your guitar directly into the mic jack (with out the amp), but guitars, stereos, keyboards and other Line level devices produce higher voltage output. Too much source signal for mic input.