Global Payments Inc GPN.Nfell 6.7% after the company forecast full-year revenue below estimates. By Amruta Khandekar Oct 31 (Reuters) - U.S. stocks fell on Monday, potentially stalling a two-week rally in the S&P 500 and the Nasdaq indexes, as investors turned cautious ahead of the Federal Reserve's rate-setting meeting this week. A policy decision from the Fed is due on Wednesday, with investors expecting a fourth straight 75-basis point interest rate hike to curb decades-high inflation.