If you ended up installing Mint in non-UEFI mode, with Windows installed in UEFI mode, the best option is to re-install Mint, making sure that it is installed in UEFI mode.
Unfortunately, that tutorial you linked is telling you to use the Universal USB Installer - which is probably fine for non-UEFI installations, but may be problematic for UEFI.
The problem is that programs like that do not always accomodate the EFI code built into the .iso file correctly.
The most reliable methods to boot an .iso in UEFI mode is to:
A) boot the .iso itself using Windows:
http://forums.linuxmint.com/viewtopi...122187#p671008
B) burn a DVD