External Samsung 733N Monitor detected but no display

I have a Samsung LCD (Model: 733N, Model code: LS17CMAKF/XT) connected to my mid 2007 iMac that is running Mavericks.

The iMac detects the external screen - connected via a VGA adapter - but no picture is displayed.

I have tried resetting SMC and PRAM, restarting numerous times and a different kind of screen with no luck. I have used the screen on a Windows machine with no problem. I have also contacted the manufacturer and they only have drivers for Windows for this screen. I have also tried the Samsung Syncmaster cd that came with the screen but am not able to use it as it only has .exe files on it.

When I set it up initially, it showed picture for a few seconds (long enough for me to read the 'display details' window) and then it went black. The same thing has happened with another Samsung screen and a LG screen.

This iMac has had an external screen before without a problem but unfortunately I cannot use that screen anymore so I am trying to get this one to work.

Any ideas?????