Issues installing

Hello, I have purchased the theme called thunder http://themeforest.net/item/thunder-responsive-multipurpose-theme/5466969?WT.ac=emailpurchase_item&ref=emailreceipt&ref=emailreceipt&clickthrough_id=172973136&redirect_back=true

I am having issues installing it the same way I have installed every other theme I have worked with, through the WP install theme menu. When I select the zip file it starts installing, but when it reaches 100% it says “are you sure you want to do that?” I have tried installing it through FTP but have not had any luck.

I purchased the theme nearly 2 months ago and would like to get it installed:)

I appreciate any ideas offered:) As you can tell I have tried for a while on my own off and on. I am quite busy and my website is just a hobby of mine.

Thanks