There is a folder created in "My Documents" called AlienFX.
If that isn't there, my best recommendation would be to reinstall the Alien Command Center.
You can find it here.

Thank you for the reply. The folder in the documents library with my themes is still there but all the pre-installed themes are missing. My computer came with purple set as the default and a lot of other basic and advanced themes. Those are the ones that  have vanished. The link to the Command Center download is for a mid-2011 model, mine is mid-2012. I can't find a download for it anywhere. It's not listed when I go to the support page for Drivers and Downloads under my service tag.

The Mid 2011 and 2012 aren't too far apart.
Give that one a try, if it doesn't work.
Let me know and I'll try and find something more suitable.

Thank you but I would prefer not to install something on my computer that might not work. I'll just deal with the one I already have installed since the right one for my computer appears to be unavailable.