Canon Ixus-I 4.0 Meg

Do what the pros do....use a card reader instead of the camera. When you plug it into the USB port, an icon will appear called "NO NAME". Double-click on it and the pics will open in "preview". From there, you can import them to a folder you create on your desktop or into iPhoto.

If the camera is showing a black or distorted screen when set to photo, and photos that are taken with the black screen also show up black or distorted, then this would likely be a CCD imager failure, a common occurrence for your model camera.
If so, Canon should fix this for you for free, including free shipping both ways. This is regardless of your camera's warranty status.Please check this linkfor more info.

Try to see If you can see a photo in Playback mode from your memory card (Transfer a good photo to the card first) Do all the menus display correctly? If so it would seem the camera sensor (ccd) is bad. Canon had a recall on these models with bad sensors and will repair them free of charge.

Try pressing "DISP." which is the small button on the bottom left under the thumb-wheel. That turns on or off the LCD in shooting mode. In Playback mode, it shows shooting information etc.

There is recall on this model for this problem, Go to Canon USA web site, Look up Service advisory, CCD malfunction N/C to repair.

canon ixus 500.
when i switch mode to playback/preview it doesnt work so i cant view pics that are taken or can i upload them to my pc.

These are the text-only instructions:
Launching the Acer OrbiCam
To launch the Acer OrbiCam, double-click on the Acer OrbiCam logo in the
desktop.
OR
Click Start > All Programs > Acer > Acer OrbiCam. The Acer OrbiCam capture
window appears.
Changing the Acer OrbiCam settings
Resolution
To change the capture resolution, click the displayed resolution at the bottom
right corner of the capture window, then select the desired resolution.
Note: Setting the camera resolution to 640 x 480 or larger does
not change the capture window size.
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Options
Click Options to display the Window, Preview, and Folder tabs. Use the options
to change the capture window size, preview settings, and the folder for
captured photos or videos.
Camera Settings
Basic settings
Click the Camera Settings icon on the bottom right corner of the capture
display, then select Camera Settings from the pop-up menu. You can adjust the
Video, Audio, and Zoom/Face tracking options from this window.
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Capture settings
From the Camera Settings window, click the Driver Settings button. The
Properties window appears.
Device Settings allows you to change the camera brightness, contrast, hue,
saturation, sharpness, etc.
Advanced Settings allows you to activate gain control, implement image mirror,
select image enhancements and anti-flicker settings, and turn on/off the camera
indicator.
Zoom/Face Track Settings allows you to adjust the zoom level and turn the
face-tracking feature on or off.
Capturing photos/videos
To capture a photo or a video clip, rotate the Acer OrbiCam to get the desired
angle, then click the Take a Picture or Record a Video button. The Windows
Picture and Fax Viewer or the Windows Media Player automatically launches to
display/play a preview of the photo/video clip.
Note: By default, all photos and videos are saved in the My
Pictures and My Videos folder.
Using the Acer OrbiCam as webcam
The Acer OrbiCam is automatically selected as the capture device of any Instant
Messenger (IM) application. To use the Acer OrbiCam as a webcam, open the IM
service, then select the video/webcam feature. You can now broadcast from
your location to an IM partner anywhere in the world.

First, let's try the obvious. Did you accidentally hit the "DISP" button (bottom row of buttons, third from the left)?

If not, you mention you can see the photos on the PC. Do they look fine, or are they also black or distorted?

Does the camera really not take photos, or are the photos black or distorted? If black or distorted photos, then it might be a defective CCD imager. If so, Canon should fix this for you for free, including free shipping both ways. This is regardless of your camera's warranty status. Please check the following two links for more info:

http://camerarepair.blogspot.com/2007/11/canon-digital-cameras-showing-black.html

http://www.usa.canon.com/consumer/controller?act=PgComSmModDisplayAct&fcategoryid=225&modelid=13390&keycode=2112&id=29819

Applicable cameras include:
A40, A60, A70, A75, A80, A85, A95, A300, A310, S1 IS, S60, S200, S230, S330, S400, S410, S500, SD100, SD110, IXUS V2/300/400/430/500, IXY Digital 200a/300a/400/450/500

This is CCD problem that Canon know about Get onto customer support- a possible replacement camera is on the cards.