Themes messing up site

[Gashu]

Sorry! I hope this is my last help post since I'm fine with everything else on the site... it's just this.

So basically, when I try to install a custom theme (I really want the this theme: http://testsite129090343.webuda.com/index.php), it makes my whole site go completely white, and the only way I can fix it is to delete EVERYTHING and completely start over. It does this with every custom theme I try to install. I've searched the forums for people who have had the same problem, tried to follow the advice people gave them, but none of that worked either. So, I'm posting here in a last ditch effort :P

I really need help with this. I will give my login details for my site and my webhost for someone to do it for me, because I am a coding n00b, and I've exhausted all my sanity with this haha xD