Able to make continous music loop in Arduino and control the volume of the music with light sensor reading?
Having the Arduino play the audio doesn't really make sense for the scenario you describe. 

I would suggest you write an application on the PC that plays music and takes in input from and external source that is used to control the volume. You could then use the Arduino (connected via USB) to relay the light sensor readings to your PC application. The PC application then does all the "heavy lifting" since it has significantly more resources available than compared to the Arduino.