Did it say the installation failed or is it just not showing up inside 3ds Max?
If there is a Thinkbox -> Krakatoa folder in your start menu then you can use the “Add Krakatoa to 3ds Max” tool to try again. Or manually add
Krakatoa=C:\Program Files\Thinkbox\Krakatoa\3dsMax2012\Win32
to your plugin.ini for 3ds Max 2012.
It should have popped up asking for the location of 3ds Max, but its not that terrible if it didn’t. That just means that the 3ds Max plugin.ini wasn’t set to include Krakatoa when loading plugins. You should run the “Start -> All Programs -> Thinkbox -> Krakatoa 1.6 -> Add Krakatoa to 3ds Max” tool which will create the popup you are expecting.