Late 2009 imac as second monitor
Hello, I just purchased a new iMac retina 27 inch. I am trying to use my late 2009 iMac 27 inch as a second display using a mini display port. I can get it to work my old cheap second monitor, but when I try the 2009 mac, and I press command F2, it shows the options to set up as a second monitor on the new retina mac but then after a few seconds the options disappear and they go back to being separate monitors. Just wondering if anyone has been able to make this work as I'd hate to have to sell my 2009 mac. Thanks in advance.