Well, I haven't found any sure fixes for this, but u can google fatal error 7 minecraft to see more possible solutions. My suggetion, redownload/update java and try that way. Also, fatal error 7 is an applet error, so I dont know for sure, but I suspect you may be able to play on the wom client (if you haven't tried already). But if neither of those work just try that google search, there are plenty of other solutions offered, but there always seem to be complaints that they don't work, and it would be impossible/pointless for me to put all of the unproven solutions in this post.