I had my site go blank on me before too, I'm not sure what caused it though. I don't think it was anything to do with adding a theme, cause I hadn't tried installing one yet. I wasn't sure what I did to cause it either. Even after removing the /entire/ thing (luckily I hadn't yet done much work on it) and re-installing it all I still couldn't view it.
I assumed it was my at the time server which was 20m.us
Now I'm using ServersFree.com If you haven't yet gotten a new host, it's worth checking out. I haven't ran into many problems yet with it and it's got some great offers, all of them free, too! Heres a link for you to check it out
http://www.serversfree.com/server-features/