How to install OS X on an iMac?

I think you'll have to go to an Apple Store and have them totally refresh your drive with OS X, but I could be wrong. As far as I know, you can only access the OS X installer via the Apple App Store; it's not available for download any other way.

 

Do you know if you erased the recovery drive? (I didn't think that as actually possible unless you really try hard to do it...)
try booting and holding cmd-r...or maybe internet recovery? I've never used it, but I think this is the kind of situation it's designed for:
https://support.apple.com/en-us/HT201314

 

If the above doesn't work you'll have to use another computer to make a bootable USB-drive. Here (http://www.macworld.com/article/298...le-os-x-10-11-el-capitan-installer-drive.html) is one of many guides you'll easily find on google.

To do this is really easy and doesn't require that much work. No need spend time/money on some guy in an apple store.

 

You should be able to access internet recovery even with a completely blank hard drive. Boot, command + R. Instead of an apple logo you'll see a spinning globe and it'll download the recovery programs temporarily to your drive. From them you can do a clean install.

 

I suggested the Apple Store because, without knowing where the OP lives, I figured the best and cheapest option was to take his machine to the Genius Bar where they'd do an install for free. The link you posted won't work because it requires the OP to access the Apple App Store, which as far as I'm aware cannot be done on any machine that does not have OS X up and running. He doesn't even have a recovery partition. So far as I know, there's no way for his machine to install OS X without outside help.

 

https://support.apple.com/en-us/HT201314

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Also if you have a copy of an OS X dmg file, one that shipped on your iMac or later, you can use a program on Windows called TransMac. http://www.acutesystems.com/scrtm.htm

It has a 15day trial so that should give you enough time.

This will help you create a USB install disk from Windows. Just right click the USB drive from TransMac and choose Restore with Disk Image and point it towards your OSX file.

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You may 1st need to format your USB drive with GPT, the drive won't work if formatted with MBR.
In windows you can do this through the command prompt and diskpart.
Have your USB drive plugged in.

Open a cmd prompt.
diskpart
list disk
**** find the number of the disk for your USB drive
select disk 3 (<- where the number is the number listed for your USB drive)
clean
convert gpt
create partition primary

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I haven't tried this before but you could possibly download VirtualBox, install OSX virtually then you'll have access to the Mac App Store to download a copy of OSX, use Disk Utility or terminal to create a bootable USB drive then reinstall OSX on the computer.

 

Did you do this exactly? Use your .dmg. You need to format the USB for Mac :