Microsoft MSFT.O reports after the bell. By Herbert Lash and Alun John NEW YORK/LONDON, Jan 24 (Reuters) - U.S. stock indexes and the dollar were flat on Tuesday after bellwether companies posted some profit beats but warned of a tough year ahead, while data showed U.S. business activity contracted for the seventh straight month in January. S&P Global's Flash U.S. Composite Output Index last month rose to 46.6, below a reading of 50 where growth begins, and companies reported soft demand amid high inflation that remained a headwind to customer spending.