The sliders for the record levels are greyed out on my computer and the input level is inappropriate, why?
These sliders directly control the hardware. Therefore, they are only active if your hardware actually does provide gain control and the driver of your hardware implements it correctly. If your particular hardware doesn’t support it, there’s nothing that one can do about it. You should be careful to adjust the level of the signal to the correct level before it reaches your hardware (or using the controls of the hardware if it has some). Also, make sure that you are actually using the correct sound input device.