New User Question - Connecting Instruments

Love my new iMac, but I can't get my Korg (or any line in using 1/4 inch or 1/8 with adapter) to be recognized at all in or out of garage band. I have Midi working fine, but I want to use my own synth sounds for certain projects.

Also, the line in on a mac doesn't seem to work like a PC's, my headsets don't work, have to use USB. Should I be coming in from keyboard on a USB too or have others made 1/4 inch with adapter to 1/8 actually work? I'm in remote eastern europe so getting adapters/cables is not as easy as US/Canada, really like to know how anyone out there has pulled their keyboard/guitar or any other 1/4 inch sourced ... I'm starting to think my line in is broken.

Cheers-

Bruce