Genitive case or attributive noun

Solution 1:

It is generally better and clearer to use the genitive, although in some cases the meaning doesn't change. In the examples you give, as Hackworth above states, the meaning of the accounting department isn't clear.

In the restaurants of Paris vs Paris restaurants (the isn't correct before the word Paris) the meaning stays the same, so they can be used interchangeably. But the room window implies there is a window somewhere else (e.g. a car) that needs to be distinguished from the one of the room. In the window of the room there is no allusion to another place that contains a window.

The differences in meaning are quite subtle, but they are still there. The safest choice is the use of the genitive.

Solution 2:

You can say all of them except The room window. That would have to be the room’s window.

The choice between the constructions depends on context. It would be more usual to see accounting department than department of accounting. That is just as grammatical, but would be found only in special circumstances. The restaurants of Paris would be the normal form. The Paris restaurants would be unlikely: Parisian restaurants would be the more usual term. The room’s window and The window of the room might be found with more or less equal frequency, depending on the linguistic environment.