(For a Reuters live blog on U.S., UK and European stock markets, click LIVE/ or type LIVE/ in a news window.) * Futures: Dow flat, S&P down 0.41%, Nasdaq falls 1.43% Feb 23 (Reuters) - Futures tracking the tech-heavy Nasdaq index pointed to a more than 1% loss at opening on Tuesday as investors sold off high-flying tech stocks on valuation concerns ahead of Federal Reserve Chairman Jerome Powell’s testimony in Congress. At 07:01 a.m. EST, Nasdaq 100 E-minis were down 189.75 points, or 1.43%, versus a 3 point, or 0.01% gain for Dow E-minis and 16 point, or 0.41% fall for S&P 500 E-minis . (Reporting by Sruthi Shankar in Bengaluru; editing by Patrick Graham)