Am guessing for your particular model camera (Powershot A70) that you really mean that it is taking black pictures. If so, this may a defective CCD imager. 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