Intel Mac :: Won't Turn On, Get Message "must Shut Down" Before It Boots U

My wife's iMac (about 4 years old, OS is pretty up to date) won't boot up. I turn it on, get the apple logo, gray-ness "curtains" down and I get that yucky "you must turn your computer off by holding down the on button" (or someting like that) in several languages. 

Tried these, none worked: 

(1) -Shut down your Mac
-Disconnect the power cord
-Press and hold the Mac’s power button for 5 seconds
-Release the button
-Reattach the power and boot the Mac as usual

(2) -Shut down the computer.

-Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously.

-Turn on the computer.

-Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.

-Hold the keys down until the computer restarts and you hear the startup sound for the 3rd time.

-Release the keys and let your system boot up.    

(3) -Power the iMac off

-Power your iMac on and hold down the "Option" key

-Choose your internal hard drive (Macintosh HD) and boot up your iMac