Canon Power Shot A80 LCD screen not working.

This sounds like it might be a defective CCD imager, and is a known defect for your particular model camera.. If so, Canon should fix this for you for free if you live in the US, Canada, and a select few other countries. If you live outside the US, contact Canon support for your country to see if they'll still honor the advisory (some still will, especially if you stress you knowledge that this is a known defect of the camera). They may also include free shipping both ways (free shipping varies with countries). This is regardless of your camera's warranty status. Please see this link for more info.

Affected cameras with this problem include: A60, A70, A75, A80, A85, A95, A300, A310, S1 IS, S60, S230, S400, S410, S500, SD100, SD110, IXUS V2/V3/300/400/430/500/II/IIs, IXY Digital 200a/300a/320/400/450/500/30/30a

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

Seems your Canon A80 camera got known problem of bad ccd imager IC that needs to be replaced.
Canon will replace ccd imager free of cost, click Canon CCD Imager Advisory for details.
Thanks.

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

So camera doesn't give live view to take picture? and you can view old / stored  pictures OK, is it?
If yes, then it is problem of CCD imager in Canon A80 and this part needs to be replaced.
Canon will repair your A80 free of cost as per announced scheme of CCD imager support.
Click Canon CCD Advisory to know how to get free repair facility.

The matrix is dead. Probably because of an intensive light got into the lense while the camera was in night mode. It's dead. Nothing can be done.

The symptoms you describe sound like a CCD failure. Canon is fixing this for for free for certain cameras, including free shipping both ways. This is regardless of the camera's warranty status. However, the SD400 is not on the advisory list (although the S400 is). 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

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

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.
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
Also kavi, here is the info on the recall and service centers near you in India. Send the closest one an email describing your problem, and MAKE SURE THAT YOU MENTION THE ADVISORY FOR FREE REPAIR AND SHIPPING:
http://www.canon-asia.com/index.jsp?fuseaction=support&prod_type=image-phenomena_notice
http://www.canon-asia.com/index.jsp?fuseaction=contactus&prod_type=sales_service_in

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