Black LCD after switching on

My Canon 800 IS started to behave strangely a few weeks ago. When I switch it on in either A or M mode the LCD display is black (except for data like number of pictures available etc.), also no picture is taken properly. If I trun the mode wheel to picture browsing and back to A or M mode the LCD is OK, I can also use DISP button to make the LCD alive. What can be wrong and how to fix it?

First thing I would do is reset the camera. This is a fairly easy procedure which involves either going into your setup menu and choosing "reset" (or intialize), holding down the menu key for 5 seconds, or, removing the batteries for a few minutes. It may be that the firmware loading got corrupted and the camera just needs to be "rebooted," which is something that turning it on/off won't accomplish. But after which, you should have the camera reset to factory default settings.

Another tip is to go to Canon's website and look for firmware updates. Download and install them.

But if you can fix it with the wheel, I suspect you have a loose wheel there.

Yes, I tried to reset the camera but it did not work.
Also, I don't think that this is the wheel problem, as I can also make the LCD OK by pressing DISP button 2-3 times.

I could not find the firmware for this Canon IXUS 800IS camera, could anyone suggest where could it be found???

IXUS is a European model. Check the Canon Europe site.