Today, for no reason, Bluetooth support stopped on my 27″ iMac, disconnecting my Magic Trackpad and taking out the icon in the System Preferences…
This is one of those annoying moments that doesn’t seem to have any explanation and has been experienced by a lot of people judging by the various Mac-support forums. Any wireless device you use such as a mouse or keyboard can also go down suddenly, and Apple have a dedicated page here where you can find troubleshooting advice: Apple Bluetooth Support page.
For me, the solution was powering down for 10 minutes to flush the cache and resetting the PRAM. To do this, restart your machine and as soon as you hear the start-up sound, before you see the grey screen, press and hold cmd + alt/opt + p + r. The screen goes black and you hear the sound for a second time. Once you get to the grey load screen you can release the keys.
Christopher Parsons also has some helpful advice here on his blog.Mac OSX Apple, Keyboard shortcuts, OSX