A NEW crisis of confidence shook markets as shares in IBM were hammered to a four-year low. The Dow Jones Industrial Average, which rose 1% last week, tumbled 198.59 points or 1.98% to 9,808.04, its lowest since early February. The Nasdaq Index, starting the day down 17% on the year, slipped 34.55 points or 2.14% to 1,578.48, where it stood in October.