Hewlett-Packard Co. reported a record loss and slumping sales for personal computers and services aimed at businesses, underscoring the turnaround challenge facing CEO Meg Whitman. The third-quarter loss of $8.86 billion includes a write-down for the enterprise-services unit and reflects a 10 percent drop in PC revenue. HP pared the high end of its full-year forecast for profit to $4.07 a share, from $4.10, missing the average $4.08 analyst estimate. Almost a year into her tenure at the helm of the largest PC maker, Whitman is boosting investment in research and development and revamping the PC, printer, and enterprise-services units. HP is under pressure from rivals such as Apple Inc. in computing devices and IBM Corp. among corporate clients.