meaning of start up disk
how to start up my macbook pro 15
MacBook Pro 15″, macOS 10.13
how to start up my macbook pro 15
MacBook Pro 15″, macOS 10.13
No idea without problem details: https://discussions.apple.com/docs/DOC-5931
Assuming it's undamaged, you do so by pressing the power button. Or by lifting the lid depending on what year model it is.
The startup disk is the disk on which the OS resides.
If you press the power button and nothing happens, please read If your Mac doesn't turn on - Apple Support.
meaning of start up disk