OPTION 1:
Uninstall again and then delete the wamp folder and all sub folders.
This will remove the mysql database that you changed when you added a password. Then reinstall.
OPTION 2:
I think wamp tries not to scrap your mysql databases when you reinstall so the password will still be set for root.
change the config.inc.php file again to add the password you setup for the root user.
Try reading this it may also help
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forum.wampserver.com]