You need to establish whether it is your installation or what you are importing.
Import a topic from one of the sample projects as we know they are OK. Click Open on the RoboHelp Starter page and then click Samples in the ribbon on the left.
If that fails, there is something wrong with your installation. If it succeeds, then the problem is related to what you are importing.
Come back when you know which it is.
See www.grainge.org for RoboHelp and Authoring tips
Does it seem to hang immediately upon choosing to import? Do you see the import dialog or does it hang after choosing a file?
If you aren't even seeing the dialog and if you have a keyboard that has a key with a Windows logo on it, press and hold the windows logo key as you press the left arrow key a couple of times.
If your keyboard doesn't have a Windows logo key, press alt+spacebar. Then press M followed by pressing any arrow key. Then wiggle your mouse a bit and the dialog should pop into the viewable space.