|"Everything is installed correctly. I didn't touch anything, except as described..... "|
"....I did not find any options (playback devices, etc.) that would allow me to proceed with my turntable installation,..."
I may have mis-interpreted that. I was assuming you were not seeing the Playback and Recording devices there.
Is everything is as I described it in Response 1 - you see everything in Control Panel - (your sound brand settings), and Control Panel - Sound, and when you click on the speaker icon in your taskbar?
If you DO see those things, then your sound software is probably installed okay - something else is wrong.......
"Now I have NO SOUND AT ALL on my computer"
Obviously you must have done something un-intentionally to disable it because it was at least partially working after you had installed the turntable related software, previously. Anywhere I mention in Response 3 that has a place you can actually adjust the volume will Mute the sound if you click on the blue speaker icon there under where you can adjust it - clicking on the blue icon toggles that mute of the sound on/off - if it's muted there's a red circle icon beside the blue speaker icon.
At least one device in each of Playback and Recording must have the green circle with the white checkmark on it - the default device icon.
Your initial problems first appeared when you installed (or attempted to install ?) the software for the turntable.
It's VERY important that you have the turntable plugged into a USB port it can actually work properly in (see Response 1) , and that you installed the software for it properly, WITHOUT plugging in the USB connection until you have installed software for it first if that applies, according the the manufacturer's directions (see Response 2).
You haven't said whether you installed "drivers" for it and then installed the Audacity software, or whether you only had to install the latter. You haven't said whether you followed the manufacturer's directions.
NOTE that sometimes the resident module(s) of anti-malware programs - a part that runs all the time scanning for suspicious activity - will interfere with the proper installation of third party software, the software will not install properly, and you may get no indication of that at all while installing the software.
To avoid that possibilty, you should always DISABLE the resident module(s) of anti-malware programs, BEFORE you install third party software (software other than Microsoft Updates, etc., that dis not come with Windows ), especially when it's a major or complicated software package.
E.g. if you are using the free or paid version of AVG, you should disable the Resident Shield in AVG's 's settings in Windows. In Norton (Symantec) products, there may be several things you need to disable, or set so they don't load for a specific short amount of time.
If you don't know how to do that, tell me which anti-malware software you are using.
When you are sure the software has installed correctly, re-enable the resident module(s).
It's quite possible that's your problem with the "drivers" software for the turntable or the Audacity software.
If everthing else seems to be okay, un-install the "drivers" software for the turntable if that applies, and the Audacity software. Unplug the USB to the turntable BEFORE you un-install that - if it must be connected while un-installing the software you will get some sort of message about that. Unplug the USB to the turntable BEFORE you re-boot the computer.
Then DISABLE the resident module(s) of anti-malware programs, BEFORE you install the software again - you MAY need to leave the USB unplugged until after the "drivers" software has been installed - if you're not sure, don't plug it in initially.
If all that doesn't help....
Go to Device Manager to see if anything is flagged as not working properly.
e.g. RIGHT click on Computer, select Properties - Device Manager
Go to System Information
e.g. click on the Windows 7 icon bottom left, type: msinfo32 in the Search box, press Enter.
On the left side, select Components - Problem Devices - anything there?
On the left side, select Hardware - IRQs
Nearer the top of the list where specific devices are listed for an IRQ, e.g. about IRQ 1 to 22......
The USB controller related devices use certain IRQs. No other devices should be using one of the IRQs the USB controller related devices use, unless it's a device that's definately built into the mboard. Do you see any instances where another device other than those is using the same IRQ as the USB controller related devices? E.g. a device that's on a card in a mboard slot.
If you DO, you must fix that problem. E.g. you may need to move a card that's in a mboard slot to another slot, in order for it to NOT share an IRQ with the USB controller related devices.
Then you need to re-load the USB stack in Windows.
See the first link in Response one for further info.
When an IRQ for the USB controller related devices is shared with another device that is NOT a device that's definately built into the mboard, what usually happens is SOME USB devices work fine, SOME do not, especially likely if it's a more sophisticated device, other than a corded mouse, keyboard, or other simple device.