Nikon d3100- shutter does not go slower than 1/60?

When I'm in Aperture priority mode and I want to use about F24 with the flash on, my shutter won't go any slower than 1/60th even though the meter is showing the picture as being very under-exposed. If I have the flash ON OR OFF in Manual or Shutter priority mode the shutter will go slower than 1/60th. It is only if I have my flash OFF in Aperture priority mode the shutter will go slower than 1/60th, even though the photo is underexposed. This does not make sense.

It will if you use your camera in manual mode like a DSLR should be used. However, you have a bigger problem in that I can think of absolutely no reason why you would want to shoot at f/24, especially in lighting where you would need the flash. Sounds like you need to take a beginner's photography class…

It makes sense if your using TTL (dedicated) flash. In aperture priority mode and using TTL flash the camera will always select the shutter speed that will give a good exposure. TTL is designed for 'fill in' flash you have to alter the flash exposure to get different shutter speeds.

You have to remember with any flash shot you're taking two simultaneous exposures, one for the ambient light and one for the flash component. In any Auto mode the camera assumes you want to blend the two and will always set shutter speed and/or aperture to get a good ambient exposure.

It's all so much simpler with manual flash and manual on your camera, then you have full control.

It makes perfect sense. 1/60 is the lowest sync speed your camera will give you unless you set it to rear curtain sync. If you turn the flash on, you can't get slower that 1/60 or faster than 1/200. If you turn the flash off, you can choose any shutter speed up to 1/200, which is the maximum sync speed. That's just the way it's made.

See the chart on page 70 of your manual.

I have the D300, and the custom menu/custom settings include an option to stop the shutter from being too slow (in this case you selected 1/60) when using flash. You could reset it to a slower speed.

Also, shoot in manual, rather than P, S, or A.

I've been a professional for over twenty years, and I have never been able to get the proper exposure using any automatic setting.

One reason might be that after I take a few in an automatic mode, I'm so disappointed that I switch to manual to get exactly the image I want. I never take the time to learn how to shoot in any automatic mode.