Windows 7 Ultimate X64 Not Genuine After Years - Error 0xC004F200

My sister's computer has been running Windows 7 Ultimate x64 for more than two years. We obtained the copy from Amazon. The copy we have appears in a genuine box, with COA with interwoven holographic strip, and holographic cds. We went away camping for a week, turned on the computer on return, and the screen went black when the computer did the update check. Error code is 0xC004F200, and optional update delivery no longer works. There is an error code down the right corner, notification that build 7601, windows no longer genuine, etc.

This copy was only ever used once, and on this machine, and obtained for this machine. It has never been installed on anything else. We checked the product key via computer properties, and it said that the product key suddenly no longer matched the product key on the box/cds. On trying to change it, a dialog box came up and said that the product key has been blacklisted. We researched this, and the net said to contact microsoft.

BTW, we ran the diagnostic tool as admin.
Code:
Diagnostic Report (1.9.0027.0):
Windows Validation Data-->
Validation Code: 50
Cached Online Validation Code: 0xc004c4a2
[Code] .....