AMD, You have multiple options to choose from. First you will definitely need Windows 8 disc.. (It's up to you if you get a copy or an original, but I am in no way promoting piracy).. Then you need to go to the BIOS and change the boot options to make the laptop boot the DVD first, then follow instructions.. If everything got installed you could try and see if you can repair it, or if it's not detecting any Windows installations, then you will need to do a clean install..

Btw, it is known that by upgrading your windows 8 release preview to RTM will cause problems.. In fact that's been valid for quite some time even with older versions of Windows. It's always best to do a clean installation when going to RTM version

Hope this helps..

If everything fails you can always boot to your laptop's recovery and follow instructions to go back to factory defaults thwn start all over again..