Clicking "Update Post/Page" takes me to front-end home page, other admin issues

For almost all of today I’ve been having very weird issues with my wordpress installation.

If you go to update a post or a page that has any HTML in it, instead of actually updating, that blue button just takes you to the homepage on the front end of the website. If you create a new post/page that literally just says “test,” you’ll be fine, but start adding a link, and things get wonky.

Similar issues also occur. Sometimes the links in the left sidebar just take me to the front end of the website. When this happens, sometimes I can just try again (Go back to the Dashboard, click the same link in the left admin menu, and this time it’ll work.) With updating a post, it is 100% replicable.

As well, the way this started was when trying to add HTML to text widgets in my sidebar. But instead of taking me to the homepage, clicking “save” in the individual widget box would show a preview of the entire frontpage of the site within the widget box. It was very weird. As I started having more frustrations with not even being able to save a page/post, I didn’t see this much anywhere else, except once when trying to go to my Tools > Backups (for BackUpWordPress Backup Plugin).

Here’s what I’ve tried to know avail:

1. Disabling every plugin, including putting them in a different folder in the FTP
2. Changing the theme to Twenty Ten.
3. Doing both 1 and 2 at the same time.
4. Replacing wp-admin and wp-config.
5. Trying to repair the database using these instructions.
6. Restored my .sql file from a backup from last Sunday.

Those are pretty much in order. I can still reliably replicate on Chrome, Safari, and Firefox, including on a totally different computer. I’ve cleared browser cache and the cache of WP Super Cache. As of now I’ve lost the work I did Sunday (I was hoping the backup would have it, but alas), though I have a more recent back up I could, I suppose, restore. (Update: Restored the more recent database to at least get my work, but problem persists.)

I’m at my wit’s end! 🙁 What else is left? What exactly do I need to replace/restore? Has anyone seen anything like this before? Any help would be much appreciated!