Can't edit or add posts or leave comments

Everything seems to be frozen up on me. I may have been hacked. A new user showed up on my blog. I deleted her, but since then, I can’t post new articles, can’t edit old ones, readers can’t post comments, I can’t add new plug ins or delete old ones. I can access admin., but can’t function as admin. When I edit an old post, for example, the dashboard says edit has been updated, but then nothing updates. Same with everything else.

Also, there haven’t been any updates.

Just don’t know what to do.