Mini Disc To G5; Di To G5 Options

[mpnow]

Two related questions;

1) I have sketches of rough songs I recorded with the aid of a tiny little stereo microphone on a sony minidisc player. I would like to put them onto the hard drive of my G5. How do I do this?

2) I have been trying to start recording these sketches straight onto the mac (into Garageband) using exactly the same little microphone that I used to record onto the sony mini disc, but without any success. I do not understand why not.

I have checked that
(a) the mike still works by using it on the mini disk player again five minutes ago;
(b) in my 'system preferences' I have made sure that the 'input' is on 'audio line-in', that the volume control is up as high as it will go (though it seems to refuse to stay there and become the default volume setting);
© that the tiny little jack of the mike is plugged into the audio input jack on the back of the G5; and
(d) in Garageband, the new track is a 'real instrument' (voice).

Do not see what else I can do (I have not yet tried plugging the mike into the headphones socket on the front as I do not want to damage anything). Anyone any suggestions that will do the trick with the tools I have before me?