Both Spanish example sentences are gramatically OK, but the meaning is not exactly the same. What differs between the otherwise equivalent sentences is the topic. Your dónde-question can only be answered using the common word order you already know.
Consider what could prompt a Spanish speaker to say
Sobre el escritorio está el ordenador. (1)
El ordenador está sobre el escritorio. (2)
In (1) the computer is new information; it is volunteered by the speaker, because it presumably has not appeared in the conversation before. It is not something you would say if someone asked you about the computer; it is something you would say if you were talking about the desktop.
In (2) the computer is old information; it is in fact the thing being talked about, and the news is that it is on the desktop.
So if we were to imagine questions that would prompt the speaker to utter the first example, the one with the unusual word order, it would have to be something like
¿Qué hay sobre el escritorio?
¿Qué es eso ahí sobre el escritorio?
In Spanish, as in English and many other languages, it is often the case that the topic (or theme) of the sentence or the conversation is brought to the beginning of the sentence (this, unsurprisingly, is called topic fronting). Many times this does not change the order, because most languages place the subject at the beginning of the sentence, and the subject is often the topic. Since the topic is introduced once and then becomes old information, it is also the kind of thing that will be replaced soonest by a pronoun (in English) or deleted (in Spanish).
Fronting a complement of place is allowed in English (actual quotes):
In the middle of the road was a stocky R.A.F. officer…
All along the road were boards about ten feet high…
It is simply not allowed if the intent is to answer a question about the place. Also, it is not common usage: in general it will be replaced by a "there + be" phrase or by verbs like "lie" or "stand":
In the middle of the road stood a stocky R.A.F. officer…
All along the road there were boards about ten feet high…
These replacements are also found in Spanish (the verb haber being the usual). So Spanish and English are not that different in this respect.