Intel iMac won't boot up, please help.

Question

Yesterday I downloaded the iPhone 2.1 Software Update, I then lost two thirds of my contacts, I managed to get them back using the Sync System, I then downloaded the Security Update, which failed "Due to an error" and was "put in the Trash". My computer then crashed, I restarted it and now it won't boot up, it gets as far as the White Screen with the Apple Logo on it with the Spinning Bars "loading" icon underneath, it was like that for over an hour last night and I've tried again this morning and it's the same. has my hard drive gone or is there some less (I hope) final reason for this? Is there an equivalent to Windoze safe mode or similar?
Please help urgently.
Thank You

Answer 1

Try this qst... Safe Boot , (holding Shift key down at bootup), off the HD & use Disk Utility from there to Repair Permissions, reboot once more.
If that doesn't help, Could be many things, we should start with this...
"Try Disk Utility
1. Insert the Mac OS X Install disc that came with your computer, then restart the computer while holding the C key.
2. When your computer finishes starting up from the disc, choose Disk Utility from the Installer menu. (In Mac OS X 10.4 or later, you must select your language first.)
Important: Do not click Continue in the first screen of the Installer. If you do, you must restart from the disc again to access Disk Utility.
3. Click the First Aid tab.
4. Click the disclosure triangle to the left of the hard drive icon to display the names of your hard disk volumes and partitions.
5. Select your Mac OS X volume.
6. Click Repair. Disk Utility checks and repairs the disk."
http://docs.info.apple.com/article.html?artnum=106214
Then Safe Boot from the HD, (holding Shift key down at bootup), run Disk Utility in Applications>Utilities, then highlight your drive, click on Repair Permissions, reboot when it finishes.
The usual reason why updates fail or mess things up, or things don't load/run, is if Permissions are not fixed before & after every update, with a reboot... you may get a partial update when the installer finds it doesn't have Permissions to change one obscure little part of the OS, leaving you with a mix of OS versions.
Some people get away without Repairing Permissions for years, some for only days.
If Permissions are wrong before applying an update, you could get mixed OS versions, if Directory is the slightest messed up, who knows!
If many Permission are repaired, or any Directory errors are found, you may need to re-apply some the latest/biggest updates again, or even do an A&I if you have enough free disk space.
If we still don't have it, try without a Tiger Disk, but try fsck...
To use fsck, you must run it from the command line. Unlike using your mouse to open an application to do something, you'll need to type a text command at the prompt (#) to tell fsck what to do. The Terminal application (/Applications/Utilities) and single-user mode are two examples of command-line interfaces in which you can type such commands. To use fsck:
1. Start up your computer in single-user mode to reach the command line. Hold CMD+s keys down at bootup.
Note: If necessary, perform a forced restart as described in the Emergency Troubleshooting Handbook that came with your computer. On desktop computers, you can do this by pressing the reset/interrupt button (if there is one) or holding down the power button for several seconds. On portable computers, simultaneously press the Command-Control-power keys. If your portable computer doesn't restart with this method, you may need to reset the Power Manager.
2. At the command-line prompt, type /sbin/fsck -fy
3. Press Return. fsck will go through five "phases" and then return information about your disk's use and fragmentation. Once it finishes, it'll display this message if no issue is found:
** The volume (nameofvolume) appears to be OK 
If fsck found issues and has altered, repaired, or fixed anything, it will display this message:
*** FILE SYSTEM WAS MODIFIED *** 

Important: If this message appears, repeat the fsck command you typed in step 2 until fsck tells you that your volume appears to be OK (first-pass repairs may uncover additional issues, so this is a normal thing to do).
4. When fsck reports that your volume is OK, type reboot at the prompt and then press Return.
http://docs.info.apple.com/article.html?artnum=106214
Then Safe Boot , (holding Shift key down at bootup), off the HD & use Disk Utility from there to Repair Permissions, reboot once more.