Here are couple things to try to see which part isn't working. 1)press the menu button on the back, if the menu does show up and you can change selections using the wheel to the right then the display is ok.
2) and this is the most common, the picture CCD image sensor is bad. Make sure you have a memory card in and good batteries. Try taking a picture using the optical viewfinder. Use the slide switch to change to picture playback. If a picture shows up it may still be a bad display. Mine works fine for a while then goes black. If there is no picture or it's a purple smear then the CCD image sensor is bad. You can also try connecting it to your computer to see if there's a valid picture. Canon was replacing the CCD free of charge even after warranty ( they had gotten bad sensors from a supplier) but they may have stopped that. Send them an email from their website. They replaced the sensor on mine 5yrs after in was out of warranty.
