The Potential: HP acquired PC maker Compaq in 2002 for $25 billion to challenge Dell in the PC space, but the purchase took HP's eye off the big picture, beating IBM in servers, storage and services.
Why it Failed: The merger made HP more narrow and shareholders and Wall Street did not like it. After the deal, HP's share price dropped by a quarter. In 2005, CEO Carly Fiorina was forced to step down with shares at half the price they'd been when she started in 1999. The Compaq deal is seen as the genesis of Fiorina's troubles.