How to change the shutter speed on a nikon d5100?

When on sports mode, my camera used to take really cool action photos of people in mid air and things like that. I also liked it because it took lots of photos really quickly. Now for some reason all the photos i take on sports mode are really blurry and i can't figure out what i did wrong. All these pictures have been taken indoors so far. If the picture is focused on things close up, the shutter speed is really fast, but if it is taking a picture of something more than 5 feet away, the shutter speed is super slow. I have tried to figure this out by looking through the manual, but couldn't find any answers. Also, when i switch the view to on the screen, the shutter speed is super slow and is unfixable. Like instead of two clicks, there's only one click. Any help?

Forget using those "carry over" P&S features found on entry level dSLR's and use some basic photographic skills like shooting in manual mode.

You need to make sure that your shutter speed is 1/500th second or faster and to do that, you may have to increase the ISO setting of the camera even when shooting with the lens aperture wide open

Look on page 63 and 65 of your user manual.

I use a Nikon D5100 and here's what I do.
I shoot in Aperture mode 95% of the time. This allows me to quickly adjust the aperture using the Command Dial on the back of the camera.
I have the function button (Fn) on the front of the camera set to adjust the ISO. This allows me to quickly adjust the ISO by holding down the function button and turning the Command Dial on the back of the camera.
In Aperture mode I set the aperture for the depth of field I think I'll need. This also effects your shutter speed. Then I can easily raise and lower the shutter speed further by adjusting the ISO setting.
I generally keep my Shutter Release set to Continuous mode. This way if I hold the button down it will take several pictures and increase my chances of getting "The Shot". You need to be careful with this because it is easy to end up with literally hundreds of pictures to sort through.
The only time I use the screen on the back is to check shots after the fact or when shooting video.
You want to keep your ISO as low as possible. I try to get a shutter speed of 1/1200 or faster.
This is the set up I use to freeze birds and other animals in motion.
Hope this helps some.