If you mean that the animated Windows 8 boot screen has changed to a Vista style scan bar, this can happen (in Windows 7) after using the repair disk. It possibly applies to Windows 8 as well.
Open an elevated Command Prompt and run it as an Administrator. Type bcdboot %windir% /l en-US (note the three spaces) and press Enter. Restart the computer. To check that the locale is correct, run bcdedit.
If you use a language other than English, you need to change the en-US. Others that I know are: de-DE, fr-FR, es-ES and ja-JP.