I got a iMac from a friend and it originally had mountain lion. I was able to login and use it like normal for about 3-4 times. Then it won't log me at all.
I got apple and some other experts and was recommended to change the hard drive. I got another hard drive extacly the same size, same company etc.
I also bought snow leopard from apple store. I start the iMac and hold down the "option key" and I select the DVD installation (hard drive doesn't appear here) and when I select it then it goes to a white screen with grey apple logo and it nothing else happens from there onwards.
I can't access the iMac at all e.g. disk utility and so on.