State Dependent User Interfaces
Wow! What does that even mean? It's a pretty easy concept, but important to recognize, as this is likely the cause of almost all camera interface woes.
Basically, what the buttons and knobs and user-interface elements of a camera do are highly likely to change depending on what mode or state the camera is in.
Buttons do more than one task, depending on what other buttons are doing/what the camera feels like.
When learning how to interact with a camera, it is important to learn more than just the button, but the state of the camera that allowed this button to perform this way.
Keeping this in mind while using cameras will help one master these tools much faster!
What does this mean?
Most DSLR's have a little dial at the top of the camera. I can't speak for your camera here, but this dial changes it's behavior depending on the shooting mode.
In program mode, it may do nothing, it may adjust the relationship between shutter speed and aperture, or it may adjust the exposure compensation. In aperture priority mode, it will adjust the aperture setting. In shutter speed mode, it will adjust the shutter speed. In manual mode, it will adjust either the shutter speed or the aperture, and the dial on the back of the camera (or wherever) will adjust the other. Sometimes. Other times, there will be a little button that changes what setting the dial adjusts, depending on whether or not is is held down.
See the button above that has "AV" and a little square with a ying-yang style plus and minus in it? That's square icon stands for exposure compensation.
In program mode, holding this button down will adjust the exposure compensation. In manual mode, exposure compensation doesn't matter any more. Holding this button down instead toggles the dial so that it adjusts the aperture value. Not holding it down adjusts the shutter speed.
The Info and Display
Most digital cameras have displays. They also have buttons (usually called "INFO" or "Disp.") that one can press that will cycle through what information is shown on the screen. These options usually include: lots of camera setting info, a minimal display, an option for the display to be completely off, a histogram, and a level, if the camera such a sensor built in.
So if you can't see anything on the screen but the camera is on and working, perhaps the 'info.' button cycled the display to be off, which saves battery.
Cameras are weird, but once you get used to these features you will not only find your favorite modes and techniques for using them, but you will be switching your camera around to do what you want it to do for the specific moment. It's really effective and feels awesome when you get the hang of it.
Don't be afraid to change your camera settings. I know photographers who only shoot in aV mode or always shoot manual. That's silly. Use your camera to it's fullest extent!