The deadline that Microsoft gave Yahoo to respond to its $44.6bn (£22.4bn) takeover offer has expired.
Microsoft chief executive Steve Ballmer gave Yahoo an ultimatum to accept the billion bid last night but now he has to decide whether to walk away or begin the company's first hostile takeover battle.
Experts believe Microsoft may now seek to gain ground by trying to get supportive voices onto Yahoo's board.
If Microsoft presses ahead with the deal it must consider if it should hold firm on the price or offer a better deal to win over shareholders.
The company has spent billions creating a web search engine and technology to sell ads, and buying Internet companies such as AQuantive.
Acquiring Yahoo would give Microsoft the number two spot in the $41 billion online ad market.
Losses at Redmond, Washington-based Microsoft's Internet business widened to $228 million last quarter, and sales rose to $843 million, at the low end of company forecasts.
Agencies