Why does my Canon A3500 pictures look white when I go to view them?

First, don't use the card again until you recover! Piriform's Recuva is a free photo recovery program that will allow you to recover images and data from your cards and devices. They're the same people that make CCleaner and are pretty reputable. I don't endorse them here, I've just successfully used their software in the past.
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Refer to this service notice from Canon. If you can see icons on the LCD, and can view photos you have taken in the past, you probably have an image sensor (CCD) failure. If Canon determines this is the problem, they will repair your camera at no cost, regardless of warranty status.

This sounds like 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 this link for more info.

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 30/30a/200a/300a/D320/400/ 450/500

This sounds like 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

CCD FAILURE !!

GOOD NEWS !! u are lucky u can get it repaired free of charge from Canon even if u are out of warranty bcoz it is a manufac fault see the link and RATE ME FIXYA for help

http://www.usa.canon.com/consumer/controller?act=PgComSmModDisplayAct&fcategoryid=221&modelid=8288&keycode=2112&id=29819

EOS 400D / Rebel XTi Digital Camera
EOS 400D/Rebel XTi doesn't have live view function, so you cannot see the picture you are taking.

If it is Canon A95 camera then it has problem of bad ccd Image and needs to be replaced that part.
Canon will repair A95 for bad ccd Imager problem free of cost.
Please click Canon ccd Imager advisory for details.

The XT does not have a "live view" feature. You have to use the viewfinder.
The LCD is strictly for data and picture viewing.

Check the video setting in the set-up menu. It may be set to PAL if you are on the NTSC system, or vice versa. Also check the TV input to ensure your're on the correct channel.

Try playing back pictures you know were captured properly ( either with another properly working camera or with your camera before the problem with quality has appeared ). If the image is ok in playback but 'noisy' in capture mode then the CCD sensor is faulty /on its way out. Ask Canon if they repair CCD faults on this model free of charge.