To troubleshoot HP printer offline issues, start by checking the printer's connection to the computer or network. Ensure all cables are securely plugged in and wireless connections are stable. Next, restart both the printer and the computer to reset the connection. Update printer drivers and firmware to the latest versions. Verify printer settings and ensure it's set as the default printer. Additionally, check for any error messages on the printer display or computer. If issues persist, run the HP Print and Scan Doctor tool for automated troubleshooting. By following these steps, you can effectively diagnose and resolve HP printer offline problems.