1 - Backup all data (at least home folders but preferably whole disk) to an external disk with Carbon Copy Cloner - don't go further until you are sure everything you want to keep has been backed up and is readable
2 - Make sure your DVD drive is working
3 - Boot from OS install DVD
4 - Erase the disk
5 - Install the OS from DVD
6 - Update with Software Update
Thanks for your reply Neville. Unfortunately all my issues started when Time Machine kept failing and I received error message after error message. I was advised to clone with carbon copy cloner but even this has failed. My latest successful time machine backup was early September. It seems that my only option is to wipe the drive and start over with that backup? I was concerned it was a RAM issue but having run Rember and Memtest my RAM is apparently ok.
There is something seriously wrong if Carbon Copy Cloner fails.
Do you know that your early September backup will work?
Is there data later than this which you would like to recover?
If you have firewire and another Mac you could try Target Disk Mode?
It is for situations like this that I always split my main disk into at least 2 volumes with working OSs on each volume.
Oh dear When you say "seriously wrong" do you have any ideas what the problem is? I have run verify disk and this has continuously said the disk is fine. Repairing disk permissions did find something which was repaired but this was when the seemingly major problems started with the mac refusing to start up, just sitting at the grey apple screen or even worse the blue screen of death.
The archive and install did finally finish, and everything appears as it should do, I am feeling more confident that my hard drive is ok (or at least not completely past recovery). I've booked an appt with the Apple Genius Bar on Sunday, do you think I should just leave it alone now and let them look at it?
I appear to have done way more harm than good
The archive and install did finally finish, and everything appears as it should do
If this is so then ignore my earlier advice which was given because you said that you could not complete archive and install.
Target Disk Mode only works with firewire.
Perhaps it is OK now.