Hi guys, thanks for the replies

After about 3 hours screaming at the screen, I managed to get the OS to install.

Found out that when he tried using it, he came unagainst the password and as he couldn't figure it out, decided to restore it. Absolutely fuming with him. He had completely wiped the memory, I've had a guy come and look at it and he says there's no way of getting any of my files back. I'm most annoyed that I had thousands and thousands of photos on it - the iMac was my editing machine and also had a lot of photos that I'd spent hours restoring from tatty old prints.

So... Have now got a virtually brand new machine again, nothing on it. This has taught me the importance of keeping more than one back up - I have got about half of the original files on an external hard drive, and some on my MacBook, but will definitely be investing in a new, larger external drive to keep everything on.

I've recently moved house and am waiting for my phone line and broadband to be connected (Monday or Tuesday hopefully, although as I live on a small island I'm kinda confused as to why it takes 10 days to get connected when all the bits needed are there already!!). As soon as I'm back online I'll have to update the iMac as it's quite behind on updates etc...

Once again, thanks for the replies :-)