There are Multiples ways to Transform an image to ICO for favicon Creation Windows 8…
But if you want a way to Save it As ICO Directly from Inside Photoshop CSX on a Windows 8 System you Currently, need a to Install a Photoshop Plugin.
Download Photoshop CS5/CS6 Plugin:ICO Format for Windows
To Install it follow Readme Instructions.
Saving a file as .ico:
Save as > Format > ico