I broke something. For awhile, clicking on "save and publish" would take me to a blank page with a URL ending /EditForm.
I found a page on the forums suggesting deleting the contents (several .js files) in a "combined files" folder, so I did.
Now it's broken in a different way--clicking "save and publish" simply reloads the admin page with the same content.
Any idea what the solution is?
... update: it turns out it stemmed from [url=http://www.silverstripe.org/general-questions/show/12612]this problem[/url], and resetting page types in MySQL was the solution.