Need moar info! Does it work properly in a different browser? What browser(s) are you using, and do any of them show errors in the debug / dev tools consoles? (tip: F12 to open tools, usually)
Next step in troubleshooting might be to change your theme to one of the defaults (Twentyeleven, twentytwelve, etc) and see if the fields work properly then. If they’re still broken, disable all plugins (except for ACF of course) and test it again! Hopefully somewhere in there you can narrow down the source of the problem.
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