Have you got Audacity 1.3.7 working now?
If so, to use the Noise Removal effect, you first need to tell it what kind of noise to remove - Fortunately this is easy to do because the Noise Removal effect just needs to “hear” the noise (on its own) and then it knows what it is supposed to remove.
Find a part of your recording that has no music, no talking, no other sounds, just the noise (preferably a couple of seconds, but at least half a second of isolated noise). Select the “noise” and call up the Noise Removal effect from the Effects menu. Click on “Get Noise Profile”. The Noise Removal effect has now “heard” the noise and is ready to go.
Now select part of the track that has the music (try this out on a section first - you may need to tweak the settings for best results, so you don’t want to be waiting ages for it to process a long track).
Call up the Noise Removal effect again and enter these settings:
Noise Reduction: 18
Frequency Smoothing: 150
Attack Decay: 0.15
The last two settings you can probably leave at these values as they are about right for most kinds of material.
Making the Noise Reduction number bigger will remove more noise, but if it is too high you will start to get some unpleasant metallic ringing/bubbling kind of sounds (artefacts).
If the noise is still too high, try increasing the Noise Reduction amount.
If the metallic artefacts are too noticeable, reduce the Noise Reduction amount.
Ideally you should aim for as low a number as will remove sufficient noise.
The noise reduction effect is a useful rescue tool, but if you always need to use it, it indicates that there is a problem somewhere. If you are recording on a laptop, try running from batteries with the power supply disconnected while you record (PC laptop power supplies are notorious for causing interference),
If that does not fix it, then I would suspect the sound card - on-board sound cards in PCs are usually pretty low quality. Fortunately upgrading a bad sound card to something considerably better can be done quite cheaply. One of the least expensive upgrades is the Behringer UCA 202, (I have one and I’m very happy with it).