How to fix a mac that won't sleep

If your Mac won't go to sleep but Energy Saver settings say it should, try the following: open Terminal and type what you see above, minus the inverted commas, but with the space after the last word

The above result shows that a process is preventing sleep - it's often something to do with printers, so...

Check all print queues are clear

Turn off printer sharing

Remove redundant printers from 'Print and Scan' preferences

There...now your Mac should get a good night's sleep...zzz