Control Panel Breaks When Upgrading to 2.5.0
From Joomla! Documentation
When upgrading from 1.7.3 to 2.5.0, the Control Panel may appear "broken" after the upgrade. See the image on this page.
How to Fix
The fix is to clear your browser's cache.
- Mozilla / Firefox / Safari: hold Shift while clicking Reload, or press either Ctrl-F5 or Ctrl-R (Command-R on a Macintosh); Konqueror: click Reload or press F5; Opera: clear the cache in Tools → Preferences; Internet Explorer: hold Ctrl while clicking Refresh, or press Ctrl-F5.