Dell, the world's largest maker of personal computers, has warned that sales have missed its forecasts amid weaker demand in the US and UK.
Competition in the personal computer market is fierce
Sales were $13.9bn (£9.6bn) in the three months to the end of September, compared with a forecast of $14.10bn.
Dell, a tech industry bellwether, also said it would take a charge of $450m related to fixing faulty computers.
Shares of Dell, which is fighting stiff competition, fell more than 5% in after hours electronic trading in New York.
The company is scheduled to report third-quarter earnings figures on 10 November.
Dell has been cutting costs and looking to increase sales of more profitable products as it battles rival computer makers including Hewlett-Packard.
Analysts said that notebook computer sales had risen, but not by enough to offset a dip in demand for its larger desk top products.
Shares of Dell have been under pressure during the past few months, losing almost a fifth of their value during the third quarter as investors buy into rivals with better growth prospects.
In contrast, Hewlett-Packard's shares are up by a third this year in the wake of its appointment of a new chief executive.