Thanks for the replies.
I updated my theme earlier this week and according to my dashboard it is up to date. I tried deactivating all plugins except for WooCommerce - the site didn't freeze when I placed the order, but instead showed a strange screen that said "checkout" at the top, but with a message below to me (not the customer) to say that a new order had been placed. The message also included the following text:
"Fatal error: Class 'order_item_meta' not found in /home2/timotij4/public_html/wp-content/themes/simplicity/woocommerce/emails/email-order-items.php on line 14"
I've checked system status and all pages seem to be set up, including the "order received" page which doesn't appear when I click on "place order". I also expect a message to appear to the user regarding BACS payment, but nothing appears.
How do I check my browser console for errors?
Thanks again for your help.