Ok I came across the same problem, fresh install of 2.5.1, was missing styles from all the pages.
Whether this works for everyone or not I don’t know, certainly fixed it for me.
Logged into the admin section by going to http://sitename/wp-login
Then I clicked on settings.
Then I noticed that the ?step=2 was present on the end of my wordpress address (URL) and Blog address (URL), I simply deleted it and clicked save.
Then when the page refreshed the style was there and all problems solved.
