No output when a parameter changes [closed]

I am very new in Mathematica, but I cannot find out what is happening here, looking on the internet. I modified a previous notebook as follows:

https://dl.dropboxusercontent.com/u/8281720/modificato.nb

but it doesn't give me any output when I put $A\neq 0$. Why?

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closed as off-topic by Oleksandr R., m_goldberg, Karsten 7., ilian, KubaSep 27 at 5:33

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Have you confirmed that each of your functions generates a number? –  bobthechemist Nov 4 '13 at 16:27
What do you mean? I can here the sound typical of an error, but no error is displayed... –  usumdelphini Nov 4 '13 at 16:50
Actually, it gives me output when A is very very big! –  usumdelphini Nov 5 '13 at 14:17
I'm voting to close this question because the notebook referred to by the link has been removed, and the question is therefore meaningless. –  Oleksandr R. Sep 27 at 2:19