Black Screen after Windows start screen (Boot Camp)

Hello,

I have just upgraded to el Captian and tried to install Windows 7.

After the completing the installation and starting Windows, I see the 'Windows loading' icon however afterwhich, the screen appears to be off. The machine is still running however.

I have a imac late 2010

lastest version of OSX el captain

things I have tried to do;

-Format partition and re-install windows

-Repair disk

Any suggestions

Kind Regards

James