Air taxi Captain reported a traffic conflict with an aircraft on the runway while on final approach; when the aircraft on the runway rejected their takeoff. ATC issued a go around to the air taxi aircraft.

Narrative

On a visual approach to 27C we were given a speed and frequency and told to contact tower. The PM remarked that that was not the frequency he had expected; but tuned it and tried to contact tower getting no response. The PM went back to approach control and was given the frequency he had expected. I saw a white spot on the threshold of the runway and could not tell if it was a patch of snow or another airplane. With the confusion it took an extra moment to get the correct frequency entered and when the tower responded to us; he told us to go around. We complied and re-entered the traffic pattern being vectored for a visual approach; which was completed uneventfully.This was caused by a combination of three things: first; we were given an incorrect frequency; second; it took us an extra moment with the confusion to contact tower; third; another aircraft was lined up on the runway and after about 30 seconds rolled down the runway; aborted his takeoff; and cleared at a high speed exit.Since we could not hear what tower was saying; we don't know whether the airliner was told to line up and wait or whether he was cleared for takeoff and then had an issue. All parties: us; ATC; and the airliner took the appropriate actions and kept this from becoming a dangerous situation.