Well you activate win 8 on installation so I fail to see how you lost the ability to pin to the taskbar 'after' activation but it might be just miscommunication. Hence my question about how you installed win 8. Did you upgrade, perform a clean install from disk or use a thumbdrive?
I agree with kemical. This sounds like another of those really strange problems that comes from the Upgrade Install. This type of install is very dependent on the original OS and installed apps. Also, if there was a problem with the license or activatin of the underlying original OS, that would explain the activation problem of Win 8. As kemical states the Win 8 installation is activated as part of the installation once a valid key is added.