Apple released its OS X 10.8.5 update yesterday, offering a number of fixes for outstanding bugs, including problems with screensavers not starting, Mail not displaying messages, and several notable fixes for new Apple hardware, specifically the new MacBook Air, which showed truncated Wi-Fi networking speeds at its debut.
While for the most part the 10.8.5 update has shown improvement for people's systems, as with any updates there are a few people who have found some odd problems after installing the update, stemming from some experiencing the inability to log into their system to others noting a lack of Bluetooth and Wi-Fi connectivity.
If you have experienced these or similar problems after installing the OS X 10.8.5 update, there are several approaches you can take to try clearing them up.
First, try some basic troubleshooting steps, such as booting your system to Safe Mode by holding the shift key immediately after hearing the boot chimes at startup. This will have the system perform some maintenance routines and then load only essential system software. After booting to this mode, try restarting normally to see if the system loads and functions properly.
In addition, try performing some hardware resets on your system, such as clearing the PRAM and the system management controller to default settings, both which may contain settings that can influence how the system interacts with hardware such as the Wi-Fi controllers.
If you are still having troubles logging without using Safe Mode, then load to Safe Mode and try downloading and applying the OS X 10.8.5 combo updater to your system. This will reapply all the files updated since the release of OS X 10.8.0.
A final approach along these lines is to boot to the OS X recovery volume and reinstall OS X completely. This routine will have the same effect as reapplying the Combo updater (i.e., it will only replace system software files), but will do so for every system file and not just the updated ones. To do this, reboot your computer while holding Command-R, and then after choosing your language select the option to install OS X. Follow the onscreen instructions and when the installation is complete, your system should boot normally and hopefully log in properly this time.
This approach may also help situations where specific hardware such as Bluetooth or Wi-Fi will not turn on or otherwise function properly after updating the system. Though you may find instructions on the Web for copying specific kernel extensions and other individual system components from a backup or another system to use in your updated system, this type of procedure may lead to an unstable system that could hang or crash.
As always, if you have not yet updated your system to OS X 10.8.5, then be sure to fully back it up using Time Machine or a restorable drive cloning tool. With such a backup, should something go awry after updating, you can always restore to the backup and ensure everything is working properly before attempting to update again. Simply restoring to a prior backup in this manner will clear a number of caches and temporary files that may have adversely affected the initial update.