Since installing Audacity, I’ve lost all audio on my PC… help…
I’m using Windows XP and Audacity version 2.0.0 which I’ve upgraded via download to 2.0.6

If you are using a USB audio device, see here: http://manual.audacityteam.org/o/man/faq_playback.html#usb

Also, please be careful using Windows XP. Microsoft no longer support it, which makes it a dangerously insecure operating system.