Installing OS X on Mac without no current operating system?.

Ask the vendor for those details - or suggest he gives it back to whomsoever he stole it from.

You may have to contact Apple (main support or applecare) to see if there was any software on DVD media for that model, if there is no optical drive slot, then it likely shipped with Lion 10.7 installed, but may have had backup media discs. Those would be available by serial number and product model number descriptions; so if you do call or contact Apple, have those indentifiers handy. These may be on the foot of the iMac, bottom of the stand.

Also, it may not be legit. Find serial numbers - other than logic board:

http://support.apple.com/kb/HT1750?viewlocale=en_US&locale=en_US

The hard disk drive may be accessed by another Mac, if the computer has a Thunderbolt port and if you have a Thunderbolt to FireWire cable (or thunderbolt-thunderbolt?) so as to use another Mac to go into the iMac and check the HDD formatting, etc. Target Disk Mode. And perhaps be able to go to the Mac Apps Store to get a suitable OS X download. Usually those require a base system, so that is a hitch, so whatever the computer had on the hard disk drive in Recovery partition (if totally erased) would be needed. Online Recovery may work.

Since my antiques do not use Recovery, you may have to read up on that option.

Good luck & happy computing! 🙂

The serial number is indeed on the bottom of the foot unless it was removed by someone http://support.apple.com/kb/HT1750

If you could get the computer to start in Target Disk Mode, there may be a chance to see that model's information from another computer; but maybe not. Essentially if the unit has no optical drive (newer ones don't, so if there was a DVD, it would require an external USB optical drive) the media DVD for the computer would likely require a serial number in order to get the correct disc from Apple support by phone.

At some point, there is no later DVD to try or use, since the later OS X media is not on a DVD. It is online and you'd use Recovery online to get it. Or if the computer still has a Recovery partition, you'd have to try & see if Opt key on startup for startup manager, or Cmd + R (?) for Recovery to get there. (not sure, don't have it)

http://www.apple.com/osx/recovery/

recovery assistant:

http://support.apple.com/kb/HT4848

There may be some obscure command that may force a screen to appear in Terminal or a Firmware screen that may also have a serial number.

Haven't found it yet.

Good luck & happy computing! 🙂

If there's no drive showing up in Disk Utility then my guess is the seller sold you a Mac with a failed hard drive.

Even a blank hard drive will show up in disk utility in order to partition and format it in order to install OS X.

To the nearest Apple Store for a proper diagnostic and possibly a hard drive replacement. Just to be safe you might want to take your bill of sale from the university just to be able to prove ownership.