When I start up iMac shows question mark

There are four general causes of this issue:

1. The computer's PRAM no longer contains a valid startup disk setting when there aren't any problems with the disk itself. This can be checked for by pressing the Option key and seeing if the drive appears.

2. The internal drive's directory structure has become damaged. This requires usage of an alternate bootable system to perform the repair.

3. Critical system files have been deleted. This requires usage of an alternate bootable system to reinstall them.

4. The internal drive has died or become unplugged. This is the most likely case if the computer took a sharp impact or there are unusual sounds coming from the hard drive's location.

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(post deleted -- don't know how some of these folks respond so fast)

Reinstalling Lion Without Erasing the Drive

Boot to the Recovery HD: Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.

Repair the Hard Drive and Permissions: Upon startup select Disk Utility from the main menu. Repair the Hard Drive and Permissions as follows.

When the recovery menu appears select Disk Utility. After DU loads select your hard drive entry (mfgr.'s ID and drive size) from the the left side list. In the DU status area you will see an entry for the S.M.A.R.T. status of the hard drive. If it does not say "Verified" then the hard drive is failing or failed. (SMART status is not reported on external Firewire or USB drives.) If the drive is "Verified" then select your OS X volume from the list on the left (sub-entry below the drive entry,) click on the First Aid tab, then click on the Repair Disk button. If DU reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported click on the Repair Permissions button. Wait until the operation completes, then quit DU and return to the main menu.

Reinstall Lion: Select Reinstall Lion and click on the Continue button.

Reinstall Snow Leopard without erasing the drive

Do the following:

1. Repair the Hard Drive and Permissions

Boot from your Snow Leopard Installer disc. After the installer loads select your language and click on the Continue button. When the menu bar appears select Disk Utility from the Utilities menu. After DU loads select your hard drive entry (mfgr.'s ID and drive size) from the the left side list. In the DU status area you will see an entry for the S.M.A.R.T. status of the hard drive. If it does not say "Verified" then the hard drive is failing or failed. (SMART status is not reported on external Firewire or USB drives.) If the drive is "Verified" then select your OS X volume from the list on the left (sub-entry below the drive entry,) click on the First Aid tab, then click on the Repair Disk button. If DU reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported click on the Repair Permissions button. Wait until the operation completes, then quit DU and return to the installer.

If DU reports errors it cannot fix, then you will need Disk Warrior and/or Tech Tool Pro to repair the drive. If you don't have either of them or if neither of them can fix the drive, then you will need to reformat the drive and reinstall OS X.

2. Reinstall Snow Leopard

If the drive is OK then quit DU and return to the installer. Proceed with reinstalling OS X. Note that the Snow Leopard installer will not erase your drive or disturb your files. After installing a fresh copy of OS X the installer will move your Home folder, third-party applications, support items, and network preferences into the newly installed system.

Download and install the Combo Updater for the version you prefer from support.apple.com/downloads/.

Im having the same issue 😟

ive tried doing the steps above 'restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears'

but the boot manager screen does not appear. 😕

i get a lock and space to put in password.

my question is; what excatly is locked? so i know what password to use.

or am i being really ******** and not following the steps right?

thank you 😁