Hung up installation
If you are able to run the installer but the progress has halted, at first do not try to interrupt it. Sometimes OS X installations may hit a small snag or two that take a while to overcome, so initially wait it out. If the progress has not advanced after an hour, then it is time to try fixing the issue. If you are still in your main OS X installation before the system reboots to install Mavericks, then you can attempt to quit the Mavericks installer or force-quit it. Following this, reboot the system and try the installation again (open the installer in the Applications folder, or re-download it from the Mac App Store).

If the system has restarted and you are at the Mavericks installation progress with no OS running in the background, then your only option is to force-restart the system by holding the power button. This unfortunately can be risky, but in most cases should allow the system to reboot normally in the prior version of OS X. If so, then try running some general maintenance routines , and optionally download and re-apply the latest "Combo" updater for your version of OS X, before attempting the installation again.

Lastly, if you reset the system and you cannot boot to OS X again, then you will have to reinstall OS X from the recovery partition. To do this, reboot with the Command-R keys held down and then either restore your system from a backup, or use the OS X installer tool to reinstall the OS (your data and program installations should not be affected). When finished, you can then re-try the Mavericks installation.

Gave up waiting after 3 hours & rebooted. 1st reboot the spinning wheel appeared for ages so I rebooted again. Machine started no probs & all seems fine :-)
#notimpressedApple