My hard drive problems!!!!

Hi guys

I need some serious help please. A day ago my imac would not start up. When i started it up all I got was the Spinning wheel and the creeping line and the iMac turns it self off. Well after reading a lot of posts on here it seemed that the disk had corrupted. So I bought an external hard drive and made a "macintosh hd.dmg" copy on the external drive ( i know i should have backed up) and then reformatted the hard drive in the iMac. I checked that there was no errors (there was not) and then I reinstalled the os. The iMac is ok up to this point. I then tried to restore the macintosh hd.dmg" copy from the external drive to the iMac and it seems to go on ok with no errors flashing up. However when I reboot to start the restored version for the first time the iMac won't start and I get the spinning wheel again and the creeping line and the iMac turns it self off which is what it was doing in the first place.

Any ideas and advice would be appreciated as I have a load of photos and songs that need to put back on.

John