My Cannon printer MP520 Home screen is not working and will not display any thing at all.

Change display ribbon cable , and do it Yourself :)

Follow this link, all is free.
http://sites.google.com/site/bricolagesetc/home/my-experience-guide-repairing-pixma

Here is the solution:

http://sites.google.com/site/bricolagesetc/home/my-experience-guide-repairing-pixma

Change display ribbon cable.

Canon Services know perfectly this desing failure, but they never done anything for customers affected with this display cable failure...

So I found a cheap solution: Do It Yourself !
http://sites.google.com/site/bricolagesetc/home/my-experience-guide-repairing-pixma

Change the display cable
Solution an steps given here:
http://sites.google.com/site/bricolagesetc/home/my-experience-guide-repairing-pixma by Berurier

You need to reset or replace the ink level monitoring chip on these cartridges for refills to work. I know some refill kit sellers don't like to mention this to people before they buy the ink. Otherwise, I would recommend Cartridge World for ink refills because it can be messy to fill these cartridges and they always reset the chips for you.

Display cable Failure!
Go there and follow as described for repair

http://sites.google.com/site/bricolagesetc/home/my-experience-guide-repairing-pixma

You need to check firstly that the LCD connections are still connected correctly inside the printer and then you can enter service mode on the printer and run an LCD test. To open printer and run test you will need a service manual:

http://www.tradebit.com/filedetail.php/4981053-canon-pixma-mp520-printer-service-manual

go there
http://sites.google.com/site/bricolagesetc/home/my-experience-guide-repairing-pixma

all instructions for changing display cable

Turned it on, off many times as instructions suggest,
etc no dice. Reinstalled software, did everything including giving it a few taps.I was very seriously ready to buy a new one and trash this one, even checking flyers. I read where so my are having this same problem.
In my anger I started pushing all the buttons randomly and suddenly the green light stayed on.
Voila the crazy thing works fine again. Must have reset the glych somehow ?(I have no idea how)
Give it a try before giving up, who knows!!

cannon mp520 printer home pannel not working