Ah you probably have a corrupt Java installation. Download the "OFfline" installer, not the online installer. So with the offline installer you're installing from the computer, not over the internet. But remove the other installation as it's probably corrupt. http://www.java.com/en/download/manual.jsp which is about 15 MB downld file.

Your prefs folder ... can be found if you see the sample image from the instructions. For you I believe it will be the 2nd last post of that thread. So re-read through Step 2 of the link I gave.