WP 3.0.1. Screen Options Won't Return to 2 Column

I found a solution…it is a bitch of a bug. I too did what you did… chose 1 column just for curiosity then tried putting back to 2 and then couldn′t see a thing. Here is what I did:

Create a new user example (ADMIN_new) and use a different email to your present one so that you can create a new ADMIN_new.
Logout from you present admin and login using ADMIN_new.

You will see everything back to normal.
Delete the old admin if you want and there will be the option to delete all posts or pass the posts to ADMIN_new. Pass posts over to new ADMIN_new so you don′t lose your existing posts.

If you have access to your database do as follows:

1. open “Create New Post” or “Edit Post” site in your browser
2. change the screen-option “colums” to whatever isn’t selected at the moment
3. delete following usermetas in one step, then refresh your browser (reloading will recreate the fields, therefore you need to delete all listed fields before you refresh your browser):
3. a) wp_user-settings
3. b) wp_user-settings-time
3. c) meta-box-order_{posttypeWhereYouChangedTheLayOutGoesHere}
[!!!] Pay attention to only delete these fields and only where the user-ID is the ID of your user.

This worked for me in WP 3.0.1
I will not take any responsibility for any errors that will occur if you follow these steps – although one who knows how to handle databases and manipulate rows in his database will most likely not face any problems.

The “delete old admin acc” and “modify DB” method are so dangerous. It make me panic because it seems I have to do this to bring old screen option back.

Well, finally I find the solution
(1) Choose 2 column
(2) Drag those you need into empty column!

I only had to delete meta-box-order_* for this to work. I believe there were two in my case. I’m pretty familiar with the workings of the WP DB so I wasn’t all that worried about messing around in it (plus this was on a dev server :)), but, yes, it can be dangerous if you aren’t careful.

wing_hk’s fix did not work for me. It was one of the first things I tried.