Blog pages and admin area wont load. Please help

Hi there, im hoping someone can help me with this.
For some reason today when i tryed to access my blog (v2.7), the page wont load. It will eventually direct me to the parent directory though (which contains a non wordpress page).
I tried just accessing the wp-admin but that page doesnt load up either.
I’ve tested the url by putting an index.html file in there contianing “test” and it works fine so the url is ok. But for some reason i cant load up the blog, or any of its pages.
The directory and files are definately there, as i can still load up files from my gallery inside the /blog directory.
I cant think of any ways to fix this.
Can anyone offer some advice or help? I need to try and get the blog back up asap.
The last things i did (before it stopped working) was install the SEO plugin. I also verified my blog with google by putting another .html file in the directory (supplied by google)
I’m now wondering if this html file has conflicted with something? My blog was still working after i added the file last night, it was only today when i checked it again that the blog wouldnt load. Anyway, i’ve since removed the extra html file just incase.
Any help would be apprecaited.
If you need more info i’ll provide it.
Cheers