return it to the store and get one with Win 7
-Shut down Windows 8 while pressing the Shift key to completely power off.
-Power on and press F2 while the Toshiba logo is displayed to enter the UEFI Setup Menu.
-Go to the Security tab and set the "Secure Boot" setting to "Disabled".
-Go to the Advanced tab, enter "System Configuration" and set the Boot Mode to "CSM Boot."
-Press F10 to save and exit.
Now boot to your Win 7 disk and follow the setup instructions
Also, I expect Sysprep expects an MBR disk. So you probably need to use a partitioning tool to remove the GPT partitions. EaseUS has instructions here using its partition manager (free for personal use).