In order to access your dashboard, it is necessary to deactivate the plugin manually.
Complete the following steps:
1) Go to the your_wp_root/wp-content/plugins folder via FTP (http://codex.wordpress.org/FTP_Clients);
2) Find and rename "google-captcha" folder into "google-captcha1";
3) After you log into your dashboard, you can rename the folder back.
Make sure you have the correct “Site key” and “Secret key” entered on the plugin settings page. Get the correct keys you can here – https://www.google.com/recaptcha/admin#list. If you sure the keys are correct, contact our support team.
This article related to reCaptcha by BestWebSoft plugin
Additional resources: reCaptcha - User Guide
Still need help? Feel free to contact our friendly support team. Create a private ticket