I don’t know where you are getting Audacity from. Sourceforge has never distributed Linux binaries.
If you update to Linux Mint 17 you could uninstall whatever Audacity you are are using and install the “2.1.2-1~14.04” unofficial PPA from https://launchpad.net/~ubuntuhandbook1/+archive/ubuntu/audacity. This would give you the current Audacity release and may help the “already running” problem.
If it does not solve that problem, try deleting the audacity-lock- file in /var/tmp/audacity-.
If you connect a USB device while Audacity is running, restart Audacity or use Transport > Rescan Audio Devices.
To choose the Audacity playback or recording device you selected in pavucontrol, choose the “default” device in Device Toolbar or Devices Preferences.
Gale