In my Canon 4ood Even after i pressed halfway and the autofocus point has blinked to indicate focusing is done but focusing is not happening and the shutter won't fire.With manual focus i'm able to take the picture without a problem.

Use autofocus if you have a AF lens on it.

Usually you get a kit 18-55 AF lens that has a A/M switch on the side. The switch should be facing the A side so it's set on autofocus. Then you have 9 points on your viewfinder, those are the autofocus points. It should usually be set to center, because you usually want the object in center of your photo to not be blurry.
Remember to press the shutter button halfway and give some time for the autofocus to focus. Then you can press it all the way, you should have your photos nice and clear.

If you happen to have a manual focus lens, you should be watching through the viewfinder and turning the focus ring on the lens and determine if your object is in focus. It's hard at night, but get some practice at home when you have some more light so you get more familiar with the focus.

You did not say which camera body you are using, but you probably have three different auto-focus modes on you camera. You might be using the wrong one.

The modes are as follows:
AF-A Mode: Camera automatically selects single-servo autofocus when AF-A subject is stationary, continuous-servo autofocus when subject is moving. Shutter can only be released if camera is able to focus. AF-S Mode: For stationary subjects. Focus locks when shutter-release button AF-S is pressed halfway. Shutter can only be released when in-focus indicator is displayed.
AF-C Mode: For moving subjects. Camera focuses continuously while AF-C shutter-release button is pressed halfway. Photographs can be taken even when in-focus indicator is not displayed.

Hope I can help with some input to your problem. Let me suggest please that you switch the "mode" dial to "P" for program, check your ISO (I personally shoot ISO 100) and set it for a speed ISO 400 or lower. Most DSLR's use contrast to focus so a mirror, chrome, flat body of water, painted wall especially a white wall are just terrible to get an auto focus on. Also auto focus isn't going to happen in darkness unless you have (for Canon) an external Infrared auto focus assist beam. Also you could be to close to your subject as in attempting to do close up or macro photography and have over extended your lens capabilities.

You aren't doing anything wrong it's just I think that you have fallen into one or all of the above situations that auto focus just can't read being either dark, lacking contrast, or reflective surface or to close to your subject.

I wanted you to get off the full auto so you could enjoy the Rebel and expand on its features shooting in full auto turns it into a very expensive point and shooter. Shooting in "P" you can do what is called Program shift where you actually input settings into the camera before the picture is taken.

That little green dot focus confirmation will work even in manual mode so even though it might look out of focus to you if that dot is green and solid not blinking then it's in focus squeeze the shutter make the shot.

One other bit of information make sure you shut the IS off before mounting the camera on a tripod. if left on it will actually cause more vibration (that took me a while to figure out) have a great day hope this was a help sorry it took three days for me to find you with this problem Robert in Canada

Try pushing the Shutter halfway down until you get a green "go" indication, and take the pic. This forces the camera to focus, and is something you often have to do with these point and shoot automatic focusing cameras.

It's the autofocus trying to focus. Focus on something and press the shutter halfway down and nnow you can point wherever without autofocus trying to refocus

Autofocus is activated by pressing the shutter button halfway, be shure to have a EF lens in the camera, otherwise it won't make autofocus, put camera on full auto mode or "sports mode" (the running guy) and the focus settings on redictive AI Servo AF: Continuously tracks subject movement and achieves focus before the exposure starts.

This is your first SLR?

The normal procedure is to press the button halfway to get the focus. This is indicated by one or more red LEDs lighting in the viewfinder and a confirmation beep. Once you have this, you press the button fully to take the shot.

As the camera will not take a photo when not in focus, then pressing the button once and letting go will focus it, and pressing it again will take the shot.

Get used to pressing it halfway before taking your shots and it will soon become second nature to you.

Look on the left side of the lens. Make sure the button is on A for auto focus and not M for manual. OR not stuck in the middle. Hopefully that will solve the problem.

what i do is usually put it onto manual focus then back to auto focus, what it may be is that you are using the wrong lens for your subject :/

The shutter button features a two-stage action. Pressing Halfway Pressing halfway automatically sets the exposure, focus and white balance.
The indicators light or blink as follows.
Upper Indicator
" Green: Metering complete (two beeps sound)
" Orange: Flash will fire
" Blinking Orange: Camera shake warning / Insufficient exposure
Lower Indicator
" Yellow: Macro Mode / Manual Focus
" Blinking Yellow: Focusing difficulty* (single beep sounds)
* When the indicator blinks yellow, lock the focus before shooting.