Flash Will Not Fire

Try a mode other than auto, and turn off the flash. Then try taking a picture. Did it work? If so, then your flash is either shorted or burned out, or the flash safety circuit thinks that the camera is open. If the flash is burned out, then professional repair is required, as a flash change-out is not trivial (Call 1-800-OK-CANON).

However, it's more likely to be only a break in the safety circuit. Many Canon cameras use some of the screws in the camera case to serve as a means of detecting if the case is open (and thus disables the flash to prevent shock). Examine all the screws around the perimeter of your case. Are they all there and tight? If not, tighten loose screws and try moving and replacing any missing screws with one of the others that are still there.