Is it the same problem as this topic of yours:
importing audio files into a project into a separate track ?
There is an answer there, which you have not replied to. I suggest you have a look at that reply. If you reply there, please tell us what version of Audacity you have. We can’t answer questions properly without knowing that.
I’m locking this topic now, because you seem to say this problem is solved. If erratic behaviour occurs with the built-in speakers or with non-USB headphones, I would go to Dell’s site and install or reinstall the correct audio drivers for your Inspiron 7000 and Windows 8.1.
Gale