Sidebar list posts when clicked show selected one only

Hi guys,

Im new here, so hello everyone!
I’m building a new theme for a website,
essentially based on 3 phpS, index, sidebar and page …
my problem is in the sidebar, I see all the posts listed with a simple loop, it also works with the categories, i mean that if I click on a category, relative posts show correctly– but if I click on a link from the menu list, the list disappears, showing only the selected post.So i have to go back with browser to get the entire list again.
I tried googling around, but i reach no solution yet..
Any ideas?
Tnx.

I post the code from my sidebar:

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