Mac doesn't reboot after reinstall of OS X
For some reason, the NVRAM either lost the pointer to where the install package was located to run it after the boot, or the data written has some minor (or major) problem and now your Mac can't find any bootable images.

The self help options are to power it off and:


Attempt running Internet Recovery if you have an internet connection restarting your Mac and holding down the Command key and the R key (Command-R). Keep holding them until the Apple icon appears after selecting a network if needed.
Boot the Mac from an external OS (USB drive, another Mac in target mode, Lion USB installer, older OS install DVD if applicable) so you can re-run disk utility or see what might be failing.
Make a Lion Recovery USB drive from any other Mac that runs Lion or Mountain Lion and a 1GB or larger storage drive.


Apple also has lots of troubleshooting articles on the web (I linked to two of the most germane but you might need to search for others) or reach out to Apple as a service in their stores or online to get support if DIY or third party support isn't available to you.