Whitescreen for whole site

My brother just changed so that two domain names are pointing at my site.

The site loads fine, I log into wordpress fine. When I try to add a new post, or add an image, the admin goes into whitescreen + the site does too.

Both are then not accessible for a while. If I leave it an hour, it works again.

I disabled all plugins, then tried to add a post, same problem.

I tried accessing the site through both domains, and they both do the same thing.

Confused ??