my blog has been hacked….help please

hello there, i have a comprehensive site of over 100 posts and have discovered that in the last day or so or the pages on my blog have been deleted from my site – that includes my main “sales” page – not only that but I am unable to make a post or a page post on the blog, what can I do?

i have a dabatabase backup from the wp database plugin. how do i go about restoring my site to what it was before

how do i stop this happening again

thanks very much

km