Problem with icons

Hello everyone,
I am experiencing a strange problem with the icons shown on the Desktop.

As you may see in the attached screenshot, the folder icons are shown in the correct size, while the document icons are very small. If I modify the 'View options', both the folder and the document icons become bigger (or smaller), but I cannot find a way to restore the document icons to their 'correct' size.

I tried and modified all of the values in the 'View options' dialog with no success. I do not remember what I did but I did not touch or install system critical components.

Any hint?