Boot using Command + s
. Press enter
if the shell doesn't appear.
Disable discrete GPU: manually type nvram fa4ce28d-b62f-4c99-9cc3-6815686e30f9:gpu-power-prefs=%01%00%00%00
and run it.
Manually type nvram boot-args="-v"
and run it.
Reboot with sync; reboot
.
Boot using Command + r
(this time it boots fine, no grey screen).
Disable SIP: manually type csrutil disable
and run it.
Manually type nvram fa4ce28d-b62f-4c99-9cc3-6815686e30f9:gpu-power-prefs=%01%00%00%00
and run it
Manually type nvram boot-args="-v"
and run it
Reboot with sync; reboot
.
Boot using Command + s
.
Manually type /sbin/mount -uw /
and run it.
Manually type mkdir -p /System/Library/Extensions-off
and run it.
Manually type mv /System/Library/Extensions/AMDRadeonX3000.kext /System/Library/Extensions-off/
and run it.
Manually type touch /System/Library/Extensions/
and run it.
Reboot with sync; reboot
.