Screen on printer is showing a blank screen mp520

Change MP520 display cable

Solution by Berurier and all steps explained, with supplyer link for spare part at not much money !!!
http://sites.google.com/site/bricolagesetc/home/my-experience-guide-repairing-pixma

May be coincidence.
for repairing display the solution is to change ribbon cable: go there
http://sites.google.com/site/bricolagesetc/home/my-experience-guide-repairing-pixma
But probably you might have got solution before doing this.
Check supply block if you can (grey, on rear left back, after returning printer) May be necessary to buy repair manual on ebay ($2.95)

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

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

All steps and spare part link given by Berurier;

This worked for me:
1. Close the display lid as far as possible so you are just able to reach the power button.
2. Power off and back on.

Change the display flat cable

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

You'll spare time and money.

I think you have a lose connection caused by rotation of the flip up lcd screen. My MP520 does the same, but the characters display half way down when closing. I have not got round to opening it up to get to the guubings yet.

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

Change the display ribbon cable

Berurier found the solution and explains steps for repairing and where to buy spare part for this failure.

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

try turning it off and on again. the printer sometimes will power on but if the LCD still doesnt appear it could be shot already.