What can be done when a MAC refuse to boot and that the main page displays a white backgroung with a circle in it?
Perform the following manipulation.
Restart your MAC and hold down the 4 keys: ALT-CMD-P-R and keep them pressed up to the 5th 'beep' (the startup sound). Then release the 4 keys and let the MAC and then boot normally.
If it does not work, go to step below. Repair system files
For this, you must restart the Mac in "single mode" by holding down the Apple key and S (or Cmd and S, depending on the keyboard) until a black screen with white text appears.
When nothing moves make a carriage return to move to a new line starting with: / root#
Now type the command fsck -yf then do a carriage return to run the command.
Note 1: case sensitive and spaces
Note2: single mode, the keyboard is in QWERTY mode, better make numeric keypad to type the dash character.
The process will take a few minutes.
As long as the results contains "File was modified" repeat the fsck -yf command and do a carriage return.
Type reboot and do a carriage return
The Mac will restart normally. Notes that
If this is still doesn't work, then use the Mac OS X installation DVD/CD and restart the Mac holding down the
ALT key to select the CD/DVD as primary boot device,
A system repair from disk utility will then be perform.
for these informations!