Missing graphics

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I am new to C5.
I got it installed and can tet to the dashboard and add/edit content.

My problem is that ALL the icons and graphics are missing except for the large banner photo at the top of the page.

Where should the *.png files reside.

For example, let's start with logo.png.
It is present in the directory structure but it is not displayed. The pages just show the red X for a missing graphic file.