I'm trying to install Linux Mint 14.1 on my Lenovo B570, but when I try to boot the thumb drive, it displays a message: "Secure boot is not enabled" and then goes black screen. I read lots of posts on the subject, but there is one difference from other people's problems. I have Windows 7 installed (since over a year ago) and around 5 months ago I installed Kubuntu 12.10 without any problem (it was even the same flash drive). Now I'm facing the secure boot problem and I don't know what to do.
I'm not sure exactly what your problem is. But, when you boot next time, get into BIOS configuration and check up your "Secure boot" option. I'm guessing it is "disabled". If it is, then enable it. Reboot and see what will happens. If this doesn't help, then I will be here for you until it is done.