Hp2840 printer won't go online, says it is offline

You need to download the correct drivers for your printer.

reinstall the software with the cable connected and when asked choose wireless setup

For Vista wireless setup: Open your Control Panel. Choose Printers. In the Printers box it lists your printers. Hover over the wireless printer icon, right click, choose Run as Administrator, then choose Use Printer online. This should change the status of the printer to Ready (from Offline). Be sure you've chosen this printer as your default printer. Might have to do this on a regular basis.

Press Start Devices and printers Find the printer you wish to bring online If you are using windows xp- double click on the printer If you are using Windows 7 or vista- right click on the printer and select "see what's printing" Hit "printer" in the menu bar Toggle the "use printer offline selection"

Make sure printer and wireless access point/router is own.
Right click on printer and select "Use online"

Go to Start/Control Panel/Printers and faxes. Right click on the Canon icon and click on Offline turn toggle it back to Online. Please rate this answer.
Cheers
Bob

may be you should check, in first, in the control panel / printer ; right click on the icon of your printer , verifier that it isn't setup in offline mode , otherwise i don't know ....

Usualy you have to set up the wirless in the printer driver settings before you go wireless. I suggest pluging the printer in make sure the drivers are installed and before the disconnect choose these settings in your advanced printer driver settings (if it is wireless) and then disconnect and reboot.

Please make sure that printer is turn on, before doing ensure you do power cycle of printer.

Add printer on Standard TCP/IP port.