I am trying to re-install Leopard on my iMac, but everything is blocked. All that is displayed is a white screen with question mark icon. What can be done?
The question mark means that the iMac can not find the system on which to start.
Trying to restart the iMac by pressing the "Alt" key and select the drive containing the operation system may be a solution.
Using the FSCK command.
1) Re-start the iMac (hold the start button down for a few seconds if your Mac is "frozen").
2) Immediately after the startup sound, simultaneously press the CMD + S keys ... A series of lines of text scroll across the screen ... Release the keys .... And you also get a line ending with the "#" symbol.
3) Type the following command after the # symbol:
Note: Leave out a space between the "k" and "-" below.
4) If repairs are required, you will have this message:
FILE SYSTEM WAS MODIFIED
In this case retype fsck -fy until this message no longer appears!
5) fsck -fy will prompt you when everything is ok, from there simply type reboot and restart the Mac normally.