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This is a tale of a mac user who's bacon was saved by Snow Leopard in built back up software, time machine. If you do not use this feature - you MUST! How much do you value your data? All it takes is to buy an external hard drive.

I had an issue with my iMac today. I got a grey screen showing the Apple logo and the normal spinning cog icon but it did not proceed any further.

After searching a few forums on my iPod touch following advice about zapping PRAM and pressing shift on starting up to get safe mode working, removing all peripherals - I still had the same problem.

Here's how I successfully revived my Mac

You must have a Time Machine backup. Why anyone would not use this stunning life saver is beyond me.

1. Shut the Mac down.
2. Put the OSX install disk in and press C button immediately you power up - this forces start up from the DVD
3. You should get a screen offering to install Snow Leopard - Dont!
4. From the menu select Disk Utility.
5. In disk utility select Analyse disk.
6. In my case it found errors and I clicked repair
   1. Unfortunately this failed for me so I selected the format drive option
7. Next from the menu select restore from Time Machine.
   1. You will be asked to select a restore point. The most recent is likely to be the one.

This will take possibly hours but at least you are back to the point of last working backup.

Time Machine will not allow backups to proceed - solution

The restored computer has a different Mac Address to the one you had previously. Basically this means it does not think the Time Machine backups belong to it. This is fixed by doing the following.

1. Open Terminal
2. Establish the old name of your computer by typing 
   • ls /Volumes/"name of your backup drive"/Backups.backupdb
   • This returned Paul Johnson’s iMac for me
3. Next type (replace name of your backup drive & Paul Johnson’s iMac - what you got in step 2)
   • xattr -p com.apple.backupd.BackupMachineAddress /Volumes/"name of your backup drive/Backups.backupdb/Paul Johnson’s iMac"