* New home sales well short of expectations
* Microsoft climbs after announcing CEO Ballmer's retirement
* Indexes: Dow off 0.2 pct, S&P off 0.12 pct, Nasdaq up 0.14 pct
By Chuck Mikolajczak
NEW YORK, Aug 23 (Reuters) - U.S. stocks were little changed on Friday, a day after the Nasdaq stock exchange suffered a historic trading halt of roughly three hours as a result of technical problems.
Trading in thousands of U.S. stocks ground to a halt for much of Thursday after an unexplained technological problem shut down trading in Nasdaq securities, the latest prominent disruption to the operations of U.S. markets.
Chief Executive Officer Robert Greifeld said on CNBC television the Nasdaq resolved the technical issues that led to Thursday's trading halt, but cannot guarantee there would be no future problems.
Microsoft Corp was the biggest boost to the three major indexes, up 7.3 percent to $34.74 after the company said Chief Executive Steve Ballmer will retire within the next 12 months, once it completes the process of choosing his successor.
Even with the Nasdaq outage on Thursday, the S&P 500 managed to register its biggest percentage gain since Aug. 1, but was unable to close above its 50-day moving average for a fifth straight session. The mark, now at 1,659.26, has become a technical hurdle.
The benchmark index is on pace for a third straight weekly decline, as investors exercise caution amid uncertainty over how soon the Fed will begin to wind down its $85 billion a month stimulus program.
"This has been a very unique market situation with the Fed stimulus being such an important component to the market rally. This is uncharted waters for us," said Gordon Charlop, managing director at Rosenblatt Securities in New York.
"So regardless of what the move is, the fact you are someplace you haven't been before is cause for uncertainty."
The next Fed monetary policy meeting is scheduled for Sept. 17-18.
Economic data showed sales of new single-family homes in America fell by 13.4 percent in July to an annual rate of 394,000 units, well below expectations of 490,000 units.
The data weighed on homebuilder stocks, with PulteGroup down 3.9 percent to $15.69 and Toll Brothers off 3.8 percent to $31.25. The PHLX housing sector index lost 2.2 percent.
The Dow Jones industrial average fell 29.95 points or 0.2 percent, to 14,933.79, the S&P 500 lost 2.07 points or 0.12 percent, to 1,654.89 and the Nasdaq Composite added 5.238 points or 0.14 percent, to 3,643.945.
Pandora Media Inc slumped 12.4 percent to $19.01 after the Internet radio service said late Thursday that rising expenditures to acquire music and expand its sales force would push fiscal 2014 earnings below analyst expectations.
Aeropostale Inc tumbled 18.5 percent to $8.95 after the teen apparel retailer forecast a deep third quarter loss.