If you've got some problems with Unity Player, we'd recommend you to uninstall the player, that's installed on your PC. Then you need to download the latest version from the official Unity website. And you could also try to reinstall your browser (make sure it's up-to-date).
If the above mentioned recommendations do not prove to be helpful, please submit a ticket to our Support Service. Don't forget to describe your problem in details and mention your PC specifications, the OS and browser versions + a screenshot of the error message (if there are any) would also be of use.