Sorry to hear of your problems installing Power Tools.
I would advise downloading the pack again, just to eliminate a faulty installer, and try again. Also if you haven't already, please restart your computer before you try to install the content.
If this doesn't work then please contact Reallusion Support using the link below. They will be able to advise you further on the cause of this problem.
http://www.reallusion.com/CustomerSupport/User/QForm.aspx
Peter
Forum Administrator
www.reallusion.com