US regulators have stepped up their investigation into possible accounting irregularities at Dell.
Dell also delayed its second-quarter results
The computer firm has been informed by the Securities and Exchange Commission (SEC) that it is conducting a formal probe into its accounting practices.
The investigation, which had been proceeding on an informal basis, relates to whether Dell accounts dating back to 2002 were mis-stated.
Its shares fell 2.5% on Thursday as it delayed issuing third-quarter results.
The delay is due to the "complexity" of the results, partly a by-product of the SEC investigation.
"Dell continues to co-operate with the SEC and is committed to resolving all issues in connection with the investigation and regaining compliance with all SEC filing requirements as soon as possible," the firm said.