There is no image showing in the viewfinder or LCD screen, the menu comes up OK , the memory card has been changed and fresh batteries.

Your camera was one of a host of cameras that suffered from a faulty CCD chip. Check out this service advisory from Canon regarding it.

Malfunction:
It has been confirmed that the connecting parts of the internal wiring of the CCD used in affected products may become disconnected, especially if the affected products are stored or used in high-temperature and high-humidity environments. If this occurs, the signal is not output from the CCD normally in Shooting Mode, which may cause a distorted image or the absence of an image. This malfunction can be confirmed on the LCD monitor screen during shooting. The same malfunction also appears on the recorded image.

Canon's Response:
Effective immediately, and regardless of warranty status, Canon will repair, free of charge, the products listed above exhibiting the above-mentioned malfunction if Canon determines that the malfunction is caused by the CCD image sensor. Canon will also cover the cost of shipping and handling in connection with this repair.

So the good news is that Canon will fix it for FREE:

U.S. residents are kindly directed to contact the Canon Customer Support Center for further assistance at 1-800-828-4040. Support hours are Monday thru Friday - 8:00 AM to 12:00 midnight; and Saturday 10:00 AM to 8:00 PM (all times EST). Alternatively, if electronic support is preferred, please send your email to carecenter@cits.canon.com

Know this post is old, but this may be of help to others who have this problem. Yep this sounds like 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. The first link gives other people's experience and tips in submitting their cameras for repair under this advisory:

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

Thanks to all who contributed to this thread. Your help is invaluable.

I had a Canon Powershot S1IS that developed the “Black Screen of Death.”
After seeing this blog, on Jan. 28, 2008 I called the Canon Customer Support Center at 1-800-828-4040 informing them of my difficulty. The service rep immediately knew what I was talking about. He offered a refurbed unit for $180.00 which I declined. On Jan. 29, I received an e-mail containing an Evaluation Request form and another message with instructions and a prepaid Return Label. I immediately took the camera to the Canon repair facility in Elk Grove, IL. It was only a 30 minute drive. I asked for the camera to be shipped to me when the repairs were completed.

On February 5 I got an e-mail saying the repairs had been completed and the camera was shipped on Feb. 4. On the afternoon of the 5th Fed X delivered a NEW S5IS at no charge.

At the bottom of the packing list was a note:
Service details
We have examined the product according to your request and determined that there was a failure. Unfortunately, the parts needed to repair the unit are not available, so in order to minimize your inconvenience we are replacing the whole unit.

One could not have hoped for a better outcome.