I think what’s happening here is that you’re in AF-S (autofocus-single mode, not lens type, and damn Nikon for using the same abbreviation for both) and the camera isn’t getting as solid a focus lock as it wants. Switch to AF-C (autofocus-continuous) if it’s happening. In AF-S, focus has priority over shutter release, and if you’re indoors with an f/4 or f/5.6 lens you’re close to the limits of autofocus performance. So it’s trying to autofocus and it’s probably doing well enough that it looks fine in the viewfinder, but it’s not getting a solid focus confirmation. So it doesn’t actually fire the shutter. In AF-C, shutter release has priority over focus. You ordinarily do a lot of half-press the shutter release to focus in this mode, because it’s designed for shooting moving subjects, and then when you hit the release it goes with whatever it’s got.
This is the kit lens. It’s pretty damned good for a kit lens, but it doesn’t have as wide an aperture as you’d really like for this sort of shooting. If you can get your hands on an AF-S 50mm f/1.8 things will work much better.
One option with the lens you’ve got is to crank the ISO setting all the way up (3200 or 6400 I think, not sure how high the D60 goes off the top of my head) and set the camera to shoot black and white. You can get an almost film-like grainy monochrome effect which can be more pleasing than colour. This is because the digital noise when shooting colour will show as specs of red and green in the midst of dark shots, which looks horrible, but when converted to B&W just looks grainy. But even at the highest ISO, a darkish bar at f5.6 (which is what your lens is at 55mm) is going to give you long shutter times, and quite likely motion blur.
Actually, it’ll go to 5.6 well before you zoom it to 55mm; it’ll most likely go to f4 by about 24mm, f4.5 by 30mm, f5 by 35mm and jump right to f5.6 by about 40mm.
Your best bet is to use the flash, and zoom the lens with your left hand held under the camera, so as to not block the flash head with your fingers. Set the camera on Manual, f3.5 and about 1/60 to 1/80 second exposure.
Something fun to try, if you do use the flash with the camera in Manual, is to set your shutter speed very slow, 1/15 or less. The flash will freeze your subject, and the slower shutter speed will allow some very cool effects from the ambient light.
The band is playing a small bar Friday night and I’ll be trying out some of these ideas! Thank you all so much!