It probably recognizes that you already have Windows 10 installed on your machine. If you created original recovery disks of your computer (Windows 8x / 7), simply use them to recover your system to factory. Make sure that you first back up all your files before doing so because everything will get wiped out and deleted!
Also, it is important that you install the official Windows 10 as an update to Windows 7 / 8x on first install. Otherwise, you won't be able to activate your Windows 10 installation.
If you do not have any recovery disks, you can try downloading a Linux distro and install it over your existing system. Eventually, you should be able to boot from the Windows 10 USB stick.
10-05-2015 05:57 AM