luusid,
I had this problem with a server that had been built and a 3rd party dick management software had been installed i.e, Dell Open Manage array manager, uninstalled it ran diskpart with no errors, then reinstalled Array manager. All worked perfectly.
the 3rd party product takes control of the disks and disables Windows OS access to them.Diskpart s an MS tool and would only have been tested with MS disk management services.
Regards
Greg