NB: I originally posted this on SO, but I was recommended to try here – sorry for the duplicate!
I’m really baffled about this. In the last couple of days (since I was using the site last), my WordPress install has suddenly lost almost all of its formatting (only the top bar seems to work.
The CSS does seem to be loading, but its missing tons of them:
Here is the same page on another site (same version of WordPress);
I’m at a loss as to what could be causing this all of a sudden. The front end if fine, just to reiterate that.
This sounded very much like a caching problem. Specifically Browser Caching.
Knowing that WordPress core, and subsequently Administration Screens should not really be modified ever, there were two options immediately available. Either you were experiencing a bad cache or your WordPress install had “gone bad”.
Caching was just more likely.
But it sounds like you needed to re-install WordPress.
What probably happened is that you recently updated and the update went bad. This can happen because of not upgrading plugins first, or sometimes it happens because they do a bad release (that does happen).
Looks like the solution was to re-install.