I upgraded my iMac to 10.12.4 a day or so ago. Now when I turn it on rather than boot up, it just displays some kernel panic messages on the screen (which unfortunately I don't have a record off at the moment). If I then turn it off and back on again it works ok. This mainly seems to happen when it's been turned off for a while. I tried running a first aid scan on my hard drive, but that didn't spot any errors, and I can't see any errors in the console that are obvious relating to this (probably because it's not booting up when the message appears). Does anyone have any ideas of further diagnostics things I can try?