recording disabled?????

I have a backing track and want to record onto it through a microphone which I have plugged in and enabled (have checked it’s working OK) but when I play the track it says recording disabled?
Am I doing it right or is there another way to record onto the track such as is it possible to record a seperate track and then get them to play together?

have just changed settings in preferences from microphone input to microsoft sound mapper input and the microphone now works!

You cant record over an existing track (unless the newer versions can). There is no need to. you just record onto a different track and mix the two together. once youve got the mix right you can export it as a wav. or mp3 file and this will turn it into a single file.

if for whatever reason you want to see your 2 tracks as one file just import it (wav or mp3) back iinto audacity. If you do this with mp3s though, though then record more and export it again as an mp3 the sound quality will be degraded severely as it will have been compressed too many times.

or do you mean that audacity wont let you record your second track even onto a seperate track?