Juan attempted to install OS X onto an iMac by copying the hard drive of a different Mac he owns.
The prohibitory symbol. What does this indicate?

A.
The iMac is unable to find a startup disk that contains boot files.

B.
The version of OS X is not compatible with the iMac hardware.

C.
The source volume is damaged and cannot be read.

D.
A RAM module is having trouble

Explanation:

http://www.cnet.com/news/resolve-boot-issues-showing-prohibitory-sign/