New Theme Ruins my site

I have a website for graphic design; designra.com
It was previously using the Nimble Theme but I feel that it is currently the time for an upgrade.
The dashboard is not allowing me to upload themes. particularly through the theme area itself.
I managed to upload my theme that I want which is X, via the ftp and all of my pages turn completely white and will not allow me to use any of the customization options to do anything. What should I do? Does anyone know how to fix this problem?