Clicking on the app icon in the start menu, task bar icon or the start menu listings does nothing. If I click on the live tile icon in the start menu window it sort of dims the display and nothing else happens. Click on the desktop will close the start menu and frees up the machine but clicking the icon in the start menu just freezes it up.
I'm not experiencing any of that although I do see some minimal disk activity and a bit of a slow opening to completion of the live tiles such as weather and mail and so on, they seem to work fine and after the initial opening they are fast and normal as usual.
Did you perform a clean install or did you do an upgrade from a previous version?
Just now clicked on the task bar icon and a getting started with Cortana window popped up. I'm not sure whether I want to grant access to all my files or not so I haven't done anything with it yet.
That is sort of the way Cortana works, the more it knows about you and your interests the more efficient it becomes as a personal digital assistant.
I'm not sure how much information "all my files" you actually have on the Tech Preview but I would suspect they are relatively safe since it is more or less targeting your actual usage of apps rather than the files you've created with them.
Although you might see some recommendation based on some folder contents when using associated apps like music and such.