Garage Band Problems

i can't believe i'm trying to get help for this. it's such a simple problem and i'm fairly savvy with audio but this is ridiculous. here's my dilemna,

i'm trying to play my guitar through garage band. i'm using the new aluminum mac book and i hadn't tried this yet because i've been using the condenser mic to just get ideas down. now that i have ideas down sound quality is important and i want to direct inject my electric but it's just not working.

i'm using a 1/4 to 1/8 adapter on the guitar side, through a 1/8 cord into the line in jack right by the headphone jack.

and no sound. but garage band shows the wave forms when i record, yet when i playback nothing. basically no guitar sounds no matter what i do, but it records the waveform and i can see it in the sequencer and the editor. the stereo bars are bumping almost to the red and still no sound.

i've made sure to select real instrument track instead of software track.

i've tried selecting every input source and none of them work, i've cut the line-in input on in system preferences it's turned up and it picks up the sound in there too. there's a little bar that shows how much sound you're putting out and it's bumpin' away but still no sound.

i'm at a loss and i'm dying to get some real recording done. i've tried everything i know to do. i hate to bother with such a simple and fundamental portion of the program and it totally **** with me like this. i have a feeling the problem is really obvious as they usually are but anyway, hope someone can help. thx in advance.

I think the problem is down to the monitoring, you probably have none selected.
Look to the bottom right of the screen, with the 'i' selected turn on input monitoring -

Do you hear anything at all coming from Garageband? Like even the metronome click? If you don't you may need to select the appropriate output in Garageband's preferences.