The Federal Reserve's latest take on the U.S. economy put many investors into sell mode Tuesday, sending stocks mostly lower after a brief upward turn early in the day.Fed Chair Janet Yellen, speaking before Congress, said the U.S. economy has yet to recover fully, but raised the possibility the central bank could raise its key short-term interest rate sooner than currently projected.The Fed also issued a report noting that valuations for stocks in some sectors, such as social media and biotech firms, appear to be stretched, sending shares in Facebook, Twitter and LinkedIn lower.By suggesting some stocks could be overvalued, the Fed is adding to a growing belief among some market watchers that stocks are due for a pullback, said Drew Wilson, an equity analyst at Fenimore Asset Management."In this type of environment when you have a lot of uncertainty, essentially you have this equilibrium that's looking to be broken one way or another, and the Fed chair saying 'financial bubble' could do that," Wilson said.Investors had plenty more to consider, including a mostly encouraging batch of corporate earnings and economic data.The major U.S. financial market indexes were up slightly in premarket trading as JPMorgan, Goldman Sachs and Johnson & Johnson released quarterly results that exceeded Wall Street's expectations.Separate reports on U.S. retail sales and manufacturing growth also gave the market an early lift.But stock indexes diverged shortly after the market opened and then fully veered into the red about an hour into regular trading as investors began to tune into Yellen delivering the central bank's semi-annual economic report to Congress.Stocks finished the day mixed, with the Dow Jones industrial average eking out a tiny gain on the day.The Dow added 5.26 points, or 0.03 percent, to 17,060.68. The index is down slightly from its July 3 record of 17,068.65.The Standard & Poor's 500 index fell 3.82 points, or 0.2 percent, to 1,973.28. The index is down 0.6 percent from its most recent all-time high of 1,985.44 set July 3.The Nasdaq composite shed 24.03 points, or 0.5 percent, to 4,416.39.The three stock indexes are all up for the year.Bond prices barely budged. The yield on the 10-year Treasury note held steady at 2.55 percent.Several tech stocks surged in after-market trading Tuesday.Intel jumped $1.37, or 4.3 percent, to $33.08 after reporting strong second-quarter earnings and an increase to its stock buyback program. Apple and IBM rose after the former rivals announced they are teaming up to work on mobile applications in a bid to sell more iPhones and iPads to corporate customers. Apple rose $1.74, or 1.8 percent, to $97.06 in extended trading. IBM added $4.06, or 2.2 percent, to $192.55.Meanwhile, Facebook fell 73 cents, or 1.1 percent, to $67.17, while Twitter slipped 43 cents, also 1.1 percent, to $37.88. LinkedIn fell $1.19, or 0.7 percent, to $158.51.Yellen told Congress that the Fed intends to keep providing significant support to the U.S. economy to boost growth and improve labor market conditions, noting that the economic recovery is not yet complete.Employers added 288,000 jobs last month, the fifth straight month of gains above 200,000. The national unemployment rate has slid to 6.1 percent, a 5 1/2-year low.Yellen noted that if labor market conditions continue to improve more quickly than anticipated, the Fed could raise its key short-term interest rate sooner than currently projected."In light of corporate earnings being good, retail sales being good, manufacturing being good, even a data-driven Fed chairman is going to have to raise rates earlier than the market really wants," said Doug Cote, chief market strategist at Voya Investment Management. "So all the good fundamental data that should be good for the markets is also hawkish for rates."Beyond the Fed, investors are mostly focused on company earnings this week, including quarterly reports from Bank of America, eBay and Yum Brands on Wednesday.Bank earnings on Tuesday set a good tone for the latest earnings season.JPMorgan, the nation's largest bank by assets, said its second-quarter earnings fell 9 percent as revenue at its investment banking and mortgage businesses dropped. The stock gained $1.98, or 3.5 percent, to $58.27. Goldman's profit rose 5 percent, helped by record results from investment banking. Goldman gained $2.17, or 1.3 percent, to $169.17.Investors hammered companies whose quarterly results were less positive.Shares in rent-to-own retailer Aaron's tumbled 9.5 percent after the company cut its profit and revenue outlook for the second quarter, partly citing performance of its core business. The stock shed $3.19 to $30.34.Among other stocks in the news Tuesday:— Cigarette maker Reynolds American said it plans to buy rival Lorillard for about $25 billion in a deal to combine two of the nation's oldest and biggest tobacco companies. Reynolds fell $4.34, or 6.9 percent, to $58.84, while Lorillard sank $7.05, or 10.5 percent, to $60.17. Other tobacco stocks also declined: Altria Group slipped $1.59, or 3.7 percent, to $41.76, while Philip Morris International fell $1.36, or 1.6 percent, to $84.59.— Luxury goods retailer Michael Kors fell $6.23, or 7.3 percent, to $79.44 as some financial analysts cut their price target on the stock. Slowing sales growth even as the retailer cuts prices has worried some analysts.