Currently running High Sierra on laptop. Pressing the Option key at startup should get to the Startup Manager, but it is just a normal startup. Tried both Option keys, no effect. It does start in safe mode when pressing the Shift key so it appears keyboard working OK.
Any ideas?
Are you using a wired or wireless keyboard.
Can you reset the NVRAM and SMC? Those require startup keys and also might play into why the Startup Manager isn’t working.
Problem solved! - it was a bad usb memory stick. I had formatted and loaded a macOS installer onto the usb memory in order to do a clean install of macOS. It appears the Startup Manager could not recognize this usb memory and instead the machine would just boot normally.
Finally tried a different usb memory stick and then every thing worked as expected 
Don’t know why the first usb memory would not work, Disk Utility never complained, and copying the installer onto it worked normally. I may troubleshoot some more when I have time.
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Oh - and I forgot to add: its an old 2013-era MacBook Air so keyboard is wired in. And Adam - thanks for those tips, will file them away for future reference. I had forgotten about the NVRAM and some of the issues it could cause/fix. Thanks for refreshing my memory.
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