I'm pulling my hair out with this one!!

I have a Server 2012 x64 Enterprise SP2 and Win7 x86 clients, things have been working fine until recently.

Logging on to any PC I found that my GPO's didn't apply, I performed a gpupdate/force I then generated a GPReport which came up with the following error.

Group Policy Infrastructure failed due to the error listed below.

Access is denied.

Note: Due to the GP Core failure, none of the other Group Policy components processed their policy. Consequently, status information for the other components is not available.

I then ran rsop.msc on the affected pc and I have a red cross on the 'Computer Configuration' and the 'User Configuration'

As any one got any suggestions before I lose all my hair?

Thanks Tony