Who broke audacity?

[John Toliver]

Did you do ANY other work on the box?  Is this a family machine or a 
better version of the question is: Does anyone else have access to the 
machine?

As an alternative, try the sound recorder application and see if it does 
the same.  I don't know if the fact that you can play sound eliminates 
the possibility that the line in device, your sound card has stopped 
working.