If your date and time started showing incorrectly or your printer dropped off line before you had the start problem, then more than likely your 3.6 volt 1/2 AA battery died and needs replacement. You can also try resetting the PRAM and NVRAM, here's how:
To reset the PRAM you simply:
Shut down your Mac.
Locate and hold simultaneously the Command (Apple), Option, P, and R keys.
Turn on your Mac and hold the key combination before the gray screen appears.
Only release the keys after the computer restarts and you hear the startup sound for a second time.
If this doesn’t fix your issue you can take the next step which resets the NVRAM.
Restart your Mac.
Locate and hold down the Command (Apple), Option, O, and F keys.
Your Mac will boot into command line prompt.
Type the following, hitting return after each line:
Here's how to change it: http://www.satcure.co.uk/accs/imac.htm
Here's the battery or Radio Shack sells it for $20 : http://www.ebay.com/itm/Tekcell-1-2AA-3-...