Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
There may be a source for Sharp Zaurus (and similar Sharp models) repair. Yours obviously needs such a repair, since it either has a display problem, a character generator problem, or a memory error, depending upon the exact details of the letter display problem.
Would you be interested in having it repaired?