Good morning Maria,
With the information you give,
- Review ULS (Sharepoint logs)
- Clean your privacy settings for the web browser.
- Try to open the CA from other web browser and other WK or server.
- Review IIS, sometimes the CA stopped, and review bindings.
- Review services as TimeServices and check if there is any change about password.
- Try to re-run Sharepoint Configuration WIzard until the steps will finish.
I'll hope everything get solved.