CentOS - Jan 2016 - Create a boot USB Key to repair a Dual-Boot Windows 7 and CentOS 6.7 PC

Hello,

I have a dual-boot PC where Windows 7 is on one hard-drive and CentOS 6.7
is on another. Today I stupidly decided to update Windows 7 to Windows 10,
but had nothing but BSOD. I then used Windows 10 to go back to Windows 7,
but instead I again have BSOD. Anyone know how I can make a boot USB key so
that I can re-install Windows 7 and then repair GRUB?

Thank you,

Brian Bernard