There really isn't enough here in your question for anything more than a shot in the dark. In the future, and even for this question, please edit it to explain what camera and lens combo you are using, what settings are selected, what troubleshooting you've tried, if you've bumped/damaged/got wet/lent the camera to a friend/anything that might have caused physical damage...
Lacking ANY of that, please:
- Turn the camera off and remove the battery
- Replace the battery and turn the camera on, make sure a lens is attached
- Make sure the lens's Autofocus switch is set to AF
- Turn on all of the lights in the house/room or go outside during the day. Make sure there is a lot of light.
Set your camera settings to:
- AF Mode: AI Servo
- Shooting mode: Manual (M)
- Autofocus point selected: Center
Now, attempt to focus on something. Does the camera try to obtain focus? If yes, move to something else. Did the camera try to obtain focus? Good.
Now, take the shot. Your camera will have captured an image that, due to not actually setting any shot settings, is likely junk. That's not the point here - it captured a shot.
Now, let's start going backwards to what your normal settings probably are. Put the AF Mode to One Shot. Repeat this exercise. Did you get a shot? Great!
Finally, change the Shooting Mode back to whatever you normally use (Tv, Av, Sport mode...whatever). Repeat the exercise. Did you get a shot? Does it look good?
If your camera failed to product results through any of the above tests, please edit your question to explain which test you attempted, what the behavior of your camera was, and what it did not do (failure to attempt focus, failure to capture).