consider starless night as a symbol of a blank /empty mind.

Stars traditionally symbolize inspiration, hope, and guidance. However, when the speaker looks out of his window in the first stanza, he sees no stars in the sky. Likewise, their absence corresponds to the lack of inspiration he feels, and forces him to look elsewhere for an idea. At the end, as the image of the fox causes a poem to coalesce in his mind, the speaker mentions that "the window is starless still." The speaker's ability to write a poem in spite of the stars' absence suggests that the speaker doesn't need to wait for divine, lofty inspiration, and that generally inspiration doesn't need to be divine or lofty: it can be right front of him, or inside his own mind.