Proceed to Checkout button leads to blank page

When I click “Proceed to Checkout” button in my WooCommerce shopping cart, I am taken to a blank page.

Here is my error log — please advise:

error log:

/home3/yayforev/public_html/thatsaplentyfarm/error_log:
[28-Jan-2017 15:40:17 UTC] WordPress database error Duplicate key name ‘attribute_name’ for query ALTER TABLE wp_woocommerce_attribute_taxonomies ADD KEY attribute_name (attribute_name(191)) made by require(‘wp-blog-header.php’), require_once(‘wp-load.php’), require_once(‘wp-config.php’), require_once(‘wp-settings.php’), do_action(‘init’), WP_Hook->do_action, WP_Hook->apply_filters, call_user_func_array, WC_Install::check_version, WC_Install::install, WC_Install::create_tables, dbDelta
[28-Jan-2017 15:40:17 UTC] WordPress database error Duplicate key name ‘download_order_key_product’ for query ALTER TABLE wp_woocommerce_downloadable_product_permissions ADD KEY download_order_key_product (product_id,order_id,order_key(191),download_id) made by require(‘wp-blog-header.php’), require_once(‘wp-load.php’), require_once(‘wp-config.php’), require_once(‘wp-settings.php’), do_action(‘init’), WP_Hook->do_action, WP_Hook->apply_filters, call_user_func_array, WC_Install::check_version, WC_Install::install, WC_Install::create_tables, dbDelta
[28-Jan-2017 15:40:17 UTC] WordPress database error Duplicate key name ‘meta_key’ for query ALTER TABLE wp_woocommerce_order_itemmeta ADD KEY meta_key (meta_key(191)) made by require(‘wp-blog-header.php’), require_once(‘wp-load.php’), require_once(‘wp-config.php’), require_once(‘wp-settings.php’), do_action(‘init’), WP_Hook->do_action, WP_Hook->apply_filters, call_user_func_array, WC_Install::check_version, WC_Install::install, WC_Install::create_tables, dbDelta
[28-Jan-2017 15:40:17 UTC] WordPress database error Duplicate key name ‘tax_rate_country’ for query ALTER TABLE wp_woocommerce_tax_rates ADD KEY tax_rate_country (tax_rate_country(191)) made by require(‘wp-blog-header.php’), require_once(‘wp-load.php’), require_once(‘wp-config.php’), require_once(‘wp-settings.php’), do_action(‘init’), WP_Hook->do_action, WP_Hook->apply_filters, call_user_func_array, WC_Install::check_version, WC_Install::install, WC_Install::create_tables, dbDelta
[28-Jan-2017 15:40:17 UTC] WordPress database error Duplicate key name ‘tax_rate_state’ for query ALTER TABLE wp_woocommerce_tax_rates ADD KEY tax_rate_state (tax_rate_state(191)) made by require(‘wp-blog-header.php’), require_once(‘wp-load.php’), require_once(‘wp-config.php’), require_once(‘wp-settings.php’), do_action(‘init’), WP_Hook->do_action, WP_Hook->apply_filters, call_user_func_array, WC_Install::check_version, WC_Install::install, WC_Install::create_tables, dbDelta
[28-Jan-2017 15:40:17 UTC] WordPress database error Duplicate key name ‘tax_rate_class’ for query ALTER TABLE wp_woocommerce_tax_rates ADD KEY tax_rate_class (tax_rate_class(191)) made by require(‘wp-blog-header.php’), require_once(‘wp-load.php’), require_once(‘wp-config.php’), require_once(‘wp-settings.php’), do_action(‘init’), WP_Hook->do_action, WP_Hook->apply_filters, call_user_func_array, WC_Install::check_version, WC_Install::install, WC_Install::create_tables, dbDelta
[28-Jan-2017 15:40:17 UTC] WordPress database error Duplicate key name ‘location_type_code’ for query ALTER TABLE wp_woocommerce_tax_rate_locations ADD KEY location_type_code (location_type(40),location_code(90)) made by require(‘wp-blog-header.php’), require_once(‘wp-load.php’), require_once(‘wp-config.php’), require_once(‘wp-settings.php’), do_action(‘init’), WP_Hook->do_action, WP_Hook->apply_filters, call_user_func_array, WC_Install::check_version, WC_Install::install, WC_Install::create_tables, dbDelta