Hi mikeana
I've got a similar problem to yours which appeared after I replaced a broken screen on my Kindle 3 Keyboard.
I'm thinking I must have done something when I opened the Kindle that was similar to what your loose screw did to yours.
Anyway, I only had a few books which were affected by what you have nicely described as the "broken print" and I've managed to find a way around it.
This won't help with the screen savers or images within books that don't work properly, but it can make the print better in books.
If the books you want to fix are DRMed you will need to get rid of this first. I went here.
http://www.howtogeek.com/162994/how-...and-archiving/
In Calibre, select the book you want to fix from the library.
Click Convert Books.
Set the Output format to the same as the Input format.
Under Look & Feel, click Choose Font Family and select a font you like.
The tick Embed Referenced Fonts.
The go to Page Setup.
Under The Output profile list choose Mobipocket books (I chose this because it has the same screen size as a Keyboard).
Click OK.
The Calibre library will now show an extra format for the book called, for example, ORIGINAL_AZW3 or ORIGINAL_MOBI.
Transfer the non-original version to your Kindle and it should have a good font.
Hope this helps.