Canon printer suddenly offline

Mac OS X: About the Reset Printing System feature ...

http://support.apple.com/kb/HT1341?viewlocale=en_US

10.5/10.6/10.7 instructions...

In System Preferences>Fax & Print, Right click or Control+click on the Printers list Sidebar, choose Reset Printing System.

if you hold option and click the "-" tab it resets the printing system.

http://www.macosxhints.com/article.php?story=20031215144430486

Safe Boot from the HD, (holding Shift key down at bootup), run Disk Utility in Applications>Utilities, then highlight your drive, click on Repair Permissions.

Any devices that previously appeared in your Printer List and Fax List will need to be added again after resetting the printing system.

Resetting the printing system in Mac OS X 10.5.x+++

1. To use the Reset Printing System feature in Mac OS X 10.5.x, follow these steps:
2. Choose System Preferences from the Apple menu.
3. Choose Print & Fax from the View menu.
4. Control-click on list of printers on the left side of the window, then choose "Reset printing system" from the contextual menu. If you don't see a list of printers, Control-click on the text "Click + to add a printer or fax" and select "Reset printing system..." As an alternative, if you currently have one or more printers listed, you can Option-click the "-" (Remove printer) button.

http://support.apple.com/kb/ht1341

Reboot.

Could be many things, we should start with this...

"Try Disk Utility

1. Insert the Mac OS X Install disc, then restart the computer while holding the C key.

2. When your computer finishes starting up from the disc, choose Disk Utility from the Installer menu at top of the screen. (In Mac OS X 10.4 or later, you must select your language first.)

*Important: Do not click Continue in the first screen of the Installer. If you do, you must restart from the disc again to access Disk Utility.*

3. Click the First Aid tab.

4. Select your Mac OS X volume.

5. Click Repair Disk, (not Repair Permissions). Disk Utility checks and repairs the disk."

http://docs.info.apple.com/article.html?artnum=106214

Then try a Safe Boot, (holding Shift key down at bootup), run Disk Utility in Applications>Utilities, then highlight your drive, click on Repair Permissions, reboot when it completes.

(Safe boot may stay on the gray radian for a long time, let it go, it's trying to repair the Hard Drive.)

If perchance you can't find your install Disc, at least try it from the Safe Boot part onward.