My HP officejet 4300 series stopped printing and shows that it is offline. How do I get it back online?

Give this a try:
http://h10025.www1.hp.com/ewfrf/wc/document?docname=c02221706&cc=us&lc=en&dlc=en&product=1138342&tmp_track_link=ot_search

Hi,

Please follow below steps to make the printer Online

1. Click Start ->Control Panel ->Printer and Faxes
2. Right Click on the printer.
3. Select "Use printer Online"
4. Now your printer will be online for printing.

Please reply back for any queries.

Regards
Riztech

Open "Control Panel".
Open "Printers".
Click to select the printer.
Click the "offline/online" button, to mark it as "online".
Print.

unplug the printer's usb cable from computer then re-insert, leave printer switched on during process

Reinstalled the software.

In Windows Xp
Click on start and click on control panel
in control panel look at the top left and switch to classic view(unless your already in it,if ur in it then u'll see a lot of icons and not groups)double click the printers and faxes folder.
now look at the tow icons of your printer and one will say officejet 4300 series and one will say 4300 series fax.
right click the 4300 series and select set as default.
Now click on print if you still get the fax window select your printer icon in the drop down list and then the fax window will not popup.

IN VISTA
-------------
Click on the start button and in the start search box type "printers" and press the enter button.
In the printers window single left click the printer icon(4300 series,not 4300 series fax)
Then single right click the 4300 series icon and select set as default.
now close the window and try to print if u still get the fax popup then selet your printer icon in the drop down menu and it will print and not fax

If you need Vista drivers for your printer, go to HP.com to get them and see if that works.

If you open up the printer (start => settings => printers and faxes..), and look under the "printer" menu, is "use printer offline" checked? If it is, un-check it.