Microsoft may reopen talks with Yahoo! about a possible takeover, if a new board of directors is elected at the forthcoming shareholder meeting, according to a statement released yesterday.   The software giant has said it is still interested in a deal with Yahoo!, after discussions with billionaire investor Carl Icahn last week.    The on-again, off-again saga has been in the news since January, when Microsoft offered to buy Yahoo! for $47.5 billion. Yahoo!