Audacity has killed sound on my PC for other programs

I used Audacity (v2.0.0) to convert an audio tape to *.wav. My OS is Windows Vista Home Premium SP2.
Now I am able to get sound out of Audacity but not from any other program, including the log on/off Microsoft sounds (Control Panel>Sound>Sounds tab>pick one and Test)
I have disabled the USB Audio controller and rebooted. Now running Microsoft Driver Version 6.0.6002.18005. No improvement.
I have previously used Audacity to record audio tapes without impact. I use a LENOX player with USB connection to the PC to capture the music.
Is there a setting that needs to be changed to allow other programs to make sound - particularly Windows Media Player?

Firstly, the “death” of sounds on your PC has nothing to do with Audacity. It is almost certainly due to Windows assigning the USB device as the default output when you plugged in the USB device. Audacity does not control the Windows sound system, it just accesses it.

How did you do that? Did you physically unplug the USB cable? If not, try turning off the computer, unplugging the USB cable, then restarting the computer. Have you got sound back?

If sound works OK now, you can configure your sound system so that it will work with the USB device plugged in.
To do that, reconnect the USB device, wait a few moments for Windows to recognise it, then follow the instructions here to enable playback through your normal speakers/headphones: Audacity Manual

Thank you for the advice. I apologise for expressing what has happened badly - of course the issue is inside the workings of Windows but it was triggered by using Audacity.
To disable the USB Audio Controller - Control Panel>Device Manager> Sound, video and game controllers> right click USB Audio Controller>select Disable. This has the same effect as unplugging the cable.
I did unplug, rebooted and retested the system. I now have sound from the Windows OS but not Windows Media Player. I have not yet run Audacity - I want to reestablish sound via Media Player first.
My playback devices include Speakers (working OK) Realtek Digital Output and HDMI Output Device (reportedly working but not making any noise).
Any suggestions?

No, it was triggered by plugging in the “LENOX” player. If you had chosen to record with Windows Sound Recorder or other software, you would have lost sound in the same way.

As previously explained Audacity has (almost) no control over Windows sound playback. The only control it has is that its output slider (on the left here)

is intended to control the master volume control of the output device you have selected in Audacity Device Toolbar .

If there is Windows sound generally then Windows Media Player should have sound unless you have been changing its settings. I suggest you left-click the speaker icon by the system clock, then click on “Mixer”. Find the volume control for Windows Media Player, ensure it is unmuted, then turn the slider up. If other applications have no sound, look in the Mixer in the same way to check their volume slider.

After your next recording, the simplest procedure is just to unplug the USB player from the computer then if you had Windows sound before you plugged in the player, Windows sound will return.