hearing while recording

I have recorded over a 100 reords thru tuntables USB connecion. Since installing OSX 10.6.8 i have had to reset Audacity but still no sound thru the Mac.
I have set Reord and Playback to USB setting and listen to Software. Still no sound

You need to set the Audacity playback device in Device Toolbar to your Built-in Audio. Your turntable cannot play audio from the computer.