I have used Apple products for quite some time but haven't really had to get into the nitty gritty before and could use some help. I purchased a iMac Late 2012 27" from a guy who had moved his online marking companies office across the country. He had a buddy selling his stuff. When I bought the computer it was set up and running perfectly although it had the guy's email, software, and other person info still on the computer....no reinstall--Almost as if they had just turned off the computer a weeks prior and hadn't started it back up until I bought it. They had upgraded to Yosemite at some point. I booted up the computer holding Control R and was taken to Utilities. I did what I thought was correct and erased the Macintosh HD partition. I then quit utilities. I selected Reinstall Mac OS X via Wifi. I accepted user terms. The computer was checked via Apple for validity. Then given two choices to reinstall OS X. One is the Macintosh HD drive or Recovery HD (says it's locked and wont' let me select). Then the trouble begins. The computer wants the Apple ID and Password set up with the computer. I called the guy I bought it from, and he said that he didn't set it up and doesn't know it. Hence, I can't use the computer. From everything I can tell (hours of research), it appears I may be stuck...unless I manage to develop some more technical computer skills. I called a SimplyMac for assistance and they replied that unless I have the Apple ID/Password or the original receipt, they cannot help me. I have tried: 1) restarting and holding down command+option+R 2) restarting and holding down command+option+R+P 3) Erasing the main HDD (says it can't unmount the disc) 4) Trying my best to download the Lion Recovery and put it on a USB and upload via that. Must be doing it wrong. It shows up when I have to choose a HD to reinstall the OS but I would still have to input the Apple ID and password. Don't know. Not sure what to do at this point. It's quite frustrating. I am hopefully getting a copy of the receipt to match the serial number shortly. Apologies for the epistle. Any suggestions or ideas as to the easiest way to make this my computer???