Mid-2010 Macbook Pro won't boot after trying to install macOS Sierra After I ran the macOS Sierra installer to start installation, my 2010 Macbook Pro wouldn't start anymore. It would get to the grey startup screen, flash the Apple logo for a second, and then switch to a crossed circle, and periodically restart that sequence.



I got into verbose mode by starting my computer with Cmd+V and saw error messages like:

efiboot loaded from device: Acpi(PNP0A03,0)/Pci(1F12)/SATA(0,0)/HD(Part3,Sig4B75...)
efiboot file path: \System\Library\CoreServices\boot.efi
ERROR!!! Prelinked kernel corrupted
ERROR!!! Load prelinked kernel with status 0x000000000000001b
Error loading kernel cache (0x1b)
Error loading kernel cache (0x1b)
...


How do I get my computer back on track?
Try to remove the corrupted 'prelinked kernel' first, then rebuild the kextcache.

From the Recovery HD (putting your own volume's name instead of "Macintosh\ HD") try those three commands in Terminal in succession (pressing 'enter' after each): 

rm -f /Volumes/Macintosh\ HD/System/Library/PrelinkedKernels/prelinkedkernel 
touch /Volumes/Macintosh\ HD/System/Library/Extensions 
kextcache -u /Volumes/Macintosh\ HD 


See also:

man kextcache