no live preview – blank page after install

I just bought highend. I tried a live preview and got a blank page (white). I tried to activate and everything went white – no access to WP dashboard, nothing. Not a good start. I went in through bluehost and reset my theme back to the original and I think my website is back. I have an existing website not a start up.

Please tell me how to install? I prefer using a child theme. I would like to use a premade template but after reading I feel this feature is problematic – I may lose my content???

any tips