Lenovo B50-45 Notebook - Manual (Page 31)

Chapter 4. Troubleshooting
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When do I need to change the boot priority?
The default boot priorities are UEFI First. If you need to install a legacy
operating system (that is, an earlier version than that of your current
operating system) on your computer, you will need to change the boot
priority to Legacy First. The legacy operating system cannot be installed if
you do not change the boot priority.
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Getting help
How can I contact the customer support center?
See “Chapter 3. Getting help and service” of Lenovo Safety and General
Information Guide.