Bought used iMac, reinstalled snow leopard, stuck at start up screen

Question

I bought a used iMac from someone who has owned it for about a year. He had upgraded to Lion from snow leopard but I wanted to reformat everything back to the original settings(like new) so I could start from scratch. I used the original snow leopard start up discs that came with the machine and held down c when restarting, the installation went fine but when the computer restarted after the installation the apple in the grey screen appeared and the spinning circle at the bottom spun for a few seconds then froze. I let it sit over night thinking it was just taking a while to start up but in the morning it was still on the same screen, nothing had changed. Any idea what the problem is?
-Clem

Answer 1

You have to use Disk Utility to erase the ENTIRE boot drive by selecting the drive makers name on the far left, it will have the disk size too.
You need to do this to erase the 10.7 Recovery and reset the partition map back to 10.6 acceptable version so your 10.6 Disk Utility can repair the drive (and get the machine to boot) and remove the 10.7 EFI partition for 10.6 version.
I suggest you also use the Security Option > Zero all data, not for scrubbing the drive, but also for mapping off any failing sectors.
Reducing bad sectors effect on hard drives
Once 10.6 is installed, setup and Software update until clear.
then install programs, then files and only to 50% of the hard drive if possible for best performance.
don't go over 80% as it can start having issues as it gets near full.
Good Luck, setup a clone and then you can boot from the external clone drive anytime and in seconds.
Most commonly used backup methods explained