[other] All the sudden I can't boot from external HDD with other Linux Mint

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http://ubuntuforums.org – I installed Linux mint on an external hard drive and everything was going fine. I next wanted to test my windows to make sure it still worked. I set the Windows boot manager as the default boot option in the bios. Once I confirmed Windows was still working on my internal hard drive, I went back and to the bios to change the boot priority to the external drive with Linux. It seems what use to be there had disappeared. Any idea on how to get it back and have my external drive with Linux show up in the bios? (Hardware)