It is an existential question

Solution 1:

Yes the "it" refers to something concrete. Exactly what is not entirely clear, but ambiguity is not the same as existential. The questioner is probably referring to the laptop, Windows 7, the installation process or a similarly nebulous concept (Sorry David Schwartz!). The concept is only nebulous if you understand the detail and know that there are significant differences between different parts of the system giving this message.

From the questioner's perspective, the whole "laptop, process, windows" thing is a concrete object - a laptop installing Windows 7. The problem comes because what they see as a single thing others see as a set of many things. However, for the language issue as seen from the questioner's perspective, it identifies a concrete "laptop installing windows" thing that gives the error message.

Solution 2:

It most certainly can be attributed to something in particular.

"It" could be a dialog box that pops up during the install.

"It" could be a line of text, before the installer has gone into a graphical mode.

This it is ambiguous, but not existential. It could mean the laptop, Windows 7 -- two nouns that appear in the quotation -- or any number of implied entities; the installer program, a dialog box, and so on.

(I would expect that most non-technical people would conceptualise it as the laptop showing a message; the questioner is asking for clarification.).