No Signal! line in broken?

[student_trap]

hey everyone, im not sure if this is the right place to post this but searching on the topic seemed to lead me here.
basically i am trying to get some decent recordings done on my 12in powerbook, but am having a lot of trouble with its line in socket (i think this is the problem). Basically, i tried to record direct from my microphone (shure C606) but there is no signal at all coming in on the "sound" section of system prefs. assuming the signal was weak from the mic, i plugged my guitar into my amp and then my amp's line out to the powerbook, no signal again! i tried this one more time (this time using my amps headphone out), and once again no signal! when i highlight the internal microphone in sys prefs i get plenty of signal, but with the line in highlighted...nothing. Does anyone here have any ideas? do i need to "add" the microphone/guitar (as one would with a blutooth phone for example), or should it just recieve signal automatically. i tried the mic on my friends powermac G5 and there was no problems (despite the signal being weak). What am i doing wrong?

sorry for the length of this post, and thanks for any advice that you can give

 

[superbovine]

the signal needs to be amped. a lot of ppl use this.

http://www.digidesign.com/products/mbox/

 

[student_trap]

ok so i got a signal from my mac last night, not from the microphone, but from my guitar amps line out. however, the amp had to be turned up so loud that the recorded sound had lost all of the tonal qualities that i actually want to record.thanks superbovine for the reply, however the mbox, despite seeming to be a great piece of kit, is a little expensive for me, is there any other way that i could get a decent quality recording on my mac for less?