Goldman Sachs did a 180 ­degree turn on Dell Inc., Dow Jones reported, canceling its “sell” recommendation of the past two years and urging investors to buy stock in the country’s third-largest maker of personal computers. The firm also raised its price target on the stock to $13 from $9. “While we remain cautious on PC and server demand trends,” Goldman wrote, Dell has a healthy cash balance and a recent decline in the stock may have been overdone.