How to decrease input volume of levels are already at 0

I just bought a small preamp and connected it to my turntable so I could record LPs using Audacity. I hooked everything up, and the meters are pretty much slammed all the time. I moved the input slider in Audacity to 0, and I opened up to recording device control panel in Windows, selected my input device and set its level to 0, and it had no effect on the input level. Is there anything else I can try? The preamp does not have a gain knob. Should I replace it with a preamp that does have one? Is there any other way in Audacity to tone down the input?

You’ve not said how the pre-amp is connected to your computer, but I’m guessing that you have plugged the output of the pre-amp into the microphone input of your computer. That won’t work because the pre-amp signal is massively bigger than a microphone signal, and it is stereo whereas most microphone inputs are mono.

What you need to do is to plug the pre-amp output into a “stereo line level input”. If you are using a full-size computer, look on the back to see if there is a “Line Input” that you can use. The sound card inputs and outputs are often color coded:

Unfortunately, many laptop computers do not have a “stereo line level input”. If that is the case for your computer, then one solution is to get a USB stereo line level input device. Another, possibly more convenient solution is to get a USB pre-amp. One example of a low budget solution is the Behringer UFO202