After a near-panic and interminable spin, it proved impossible to get useful diagnostic information. Here are some tools and techniques which should still be useful.
startup
Another commonly-suggested panacea, Safe mode has its uses, if you understand why it is ‘safe’.
How to understand Console’s log entries for a normal shutdown, and a normal startup.
Was that crash a freeze, a panic, or just a spinning beachball? And what do they mean?
All the useful key combinations, arranged by function rather than keys.
Crowdfunding must be a good way ahead, as it is popular, and offers you something that you want. Or is it?
Sometimes, when starting up, my Mac beeps at me. What is wrong with it?
When I started my iMac up, the fan has run up to be really loud. How can I fix this?
How I can stop my Mac making its startup sound?
How much free disk space should I keep on two external hard drives, a 2 TB and a 250 GB?
The Eclectic Light Company 