Windows 7 black screen after loading screen

[DamoC]

2 out 5 times Windows loads fine but the other times after the windows loading screen and before you get to the logon screen it goes to a black screen and sits there.
I can't get to task manager, the only thing I can do is press the restart button.

Specs are:
Gigabyte Radeon 7850 running 2 x monitors
Corsair Builder Series 600w PSU
I5-3570k CPU
Gigabyte GA-Z77-D3H Mobo
Kingston 8gb DDR3
Windows 7 Home Premium

This is a new build and has has this problem since built.
I have all the latest drivers installed.

Does anybody have any suggestions please?

 

[DamoC]

Thanks for the ideas guys.
I've checked all the connections - no lose connections.
Ran sfc /scannow which found no problems.
I didn't have a fast start up option within that location or any of the power saving settings, I believe this is a Win 8 feature?

Nope it's not overclocked. The GPU is the overclocked version from standard.
https://www.overclockers.co.uk/showproduct.php?prodid=GX-100-GI