When I tried to re-install WordPress because the Visual editor stopped working when I installed any plug that would add something to it, I got an error in the layout:
So, I tried to re-install it manually, which did not solve the problem. I suspected that something is wrong with the database, so I repaired it using the built in functions. Once again, this did not work.
I think I could restore the back-up, but I would appreciate if there would be a better option to fix this issue.
EDIT: I discovered that the admin bar disappeared from the theme.