sharp Xe-A102 won't turn on,, ?

The 102 is not a long life machine. It has had lots of main board failures but these usually happen after a few years so it is to be expected on the cheapest register that Sharp make. Most of us will not sell these second hand as they are usually worn out. If it is a second hand machine that you have bought, it may have a board or printer failure. Both of which indicate end of life. If you move up to a thermal printing register, you get a much better machine in most cases.

Registerman
July 2015

manual here: http://www.hendrickxnv.be/kc/sites/default/files/downloads/XEA102fr.pdf

Unlike you, I did a Google search. This link was in the second result

X
July 2015