Here are some general steps to bring your HP Deskjet printer back online:

1. Check the connections: Ensure your printer is properly connected to your computer or network. If it is a wireless printer, check that it is connected to the correct Wi-Fi network.

2. Restart the printer: Sometimes, simply restarting the printer can solve the problem. Turn off the printer, wait for a few seconds, and then turn it back on.

3. Check printer status: On your computer, go to the 'Control Panel', then 'Devices and Printers'. Find your printer in the list, right-click on it, and see if it is set as 'Offline'. If it is, click on 'See what's printing', then click on 'Printer' in the top menu and uncheck 'Use Printer Offline'.

4. Check printer software: If the above steps don't work, there might be an issue with the printer software. Visit the HP website, find the correct drivers for your specific model, and install them.

5. Contact HP support: If none of the above steps work, it might be best to contact HP support directly. They can guide you through any more complex issues.

Please note that exact steps may vary depending on your specific printer model and the version of your operating system. These steps are a general guide and may not be exactly the same for your specific situation.