(adsbygoogle = window.adsbygoogle || []).push({}); If you've updated Windows 7 or 8 recently, it may say "This copy of Windows is not genuine", causing annoying pop-ups and wallpaper changing to black.

I had this problem on 2 pcs of mine and with a bit of searching found this fix, and it works great.

1. Run CMD as Administrator. (Search 'cmd' in the start menu, then right click and run as administrator.)
2. Type SLMGR -REARM
3. Enter.
4. Restart PC.
It should then be fixed!