Canon Rebel will not shoot in AF mode

Are you sure you did not put the AF/ MF switch in the wrong position? Although I don't think it would focus in Auto mode. In all other modes, are you sure you selected a (or more) focus point(s) in the centre of the frame?
When the selected focus point is on the side of the frame it won't focus on the parts you want it to focus. Then while pointing to the point you want the camera to focus, please press the shutter release button half and what till it focusses. Then press it the whole way down. Be aware the camera needs enough light to focus and certainly can't focus with a lens wit a min aperture of 6 or a larger number. On your 18-135 you can shoot at f16 because it will first focus on wide open and only close the aperture after you pressed the button.

Try this...remove the lens and fire off a few shots. Clean the contacts on the lens and camera body where they meet with a cotton swab lightly dampened with rubbing alcohol. Re-attach the lens and try it.

lens af unit gear is broken, or lens af saft if broken, or lens af flex is broken.
or could be camera sub mirror spring is come out from mirror unit.
take it to canon repaire centre to estimate

Most entry level SLR cameras will struggle to focus in low light, especially with the kit lens. By rights the flash should popup and emit a flash pulse to help focus. This is called focus assist. You might have to consult the manual to check if this function is turned on or not.

That is a custom function of the camera that can be change back to default with ease. While in one of the creative zones press the menu button and navigate to the 5th and final tab on the top right.
This is the Setup menu 2. In this menu, select “Custom Functions (C. Fn)” . This will open a submenu of numbered options. Select #04 and set it to 0: the default AF/AE lock on a half depress of the shutter.
That should get your camera back to the expected auto focus with the shutter button.

It is your camera using the flash to assist in focusing, if it bothers you you can change it in your menus, I have a XTi so yours will differ slightly.
Switch your camera to "P" mode.
Press "Menu" button.
Go to setup menu 3
scroll down to "Custom Functions (C Fn.)"
Press "set".
press to the right until you find "AF - assist beam"
Press "set".
And press up or down.
Set to "Does not emit"
press "set"
Press "menu" button twice.

In creative mode I would imagine that you are required to choose the focus point. Try the arrow buttons.

There are two modes to the XS's Live View system, selectable via Custom Function 7. Live View is disabled by default, by the way, so you'll need to find this menu item in Settings Menu 2 to turn it on. The two options are called Quick and Live modes. Quick mode works as most Live View modes do, dropping the mirror when you press the AE-Lock button (marked with an asterisk) to use the conventional phase-detect autofocus system. This temporarily blacks out the Live View image, which makes it impossible to know that you're still framing the subject and holding your AF point in the proper place.
That's why they added the second mode, which they call Live, but is better described as contrast-detect autofocus. This works just like a digicam, reading the image from the imaging sensor while adjusting the lens for the setting that produces the most contrast in the image. A small square appears in the center of the image area, and you can move it around with the cross keys. Just like Quick mode, unfortunately, you have to press the AE-Lock button first until you hear the focus confirmation beep, then press the shutter button to fire. It's a little slower at times than phase-detect mode, but it gets the job done. Live mode is really better for tripod work, where you can place the AF area right where you want it and confirm focus onscreen.
Both modes offer the ability to zoom in on your live view, excellent for confirming focus before capture. Using the Magnify button just right of the AE-Lock button, you can zoom in 5x or 10x, then press the AE-Lock button to focus if you like; but of course you can't confirm framing in that mode.

Try checking C.Fn III, 3: AF point selection method. Yours might still be on option 2.

0: Normal - Works by pressing the AF Point button and then the Multi-controller.

1: Multi-controller direct - Press the multi-controller to directly select an AF point (without first having to press the AF Point button). Pressing the AF button reinstates all AF points for auto AF point selection.

2: Quick Control Dial direct - turn the Quick Control Dial to select AF points. In this mode, AF points will not be displayed on the LCD panel.

AI should be focusing. You really can't change many settings when you are shooting in auto mode. Is the lens in AF mode?

I'm sure you have long since returned from vacation!

Hope this helps!