Internal Server Error

Hi, Im not techy in any way and lately i’ve noticed my website (with woo commerce plug inn) hasn’t had any sales lately and when I checked this morning any time a customer clicks on proceed to checkout an error message appears. I have no idea where to begin or whether this is a wordpress problem or a woo commerce problem so any help would be amazing.

Here’s the error message I get:-

Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator at [email protected] to inform them of the time this error occurred, and the actions you performed just before this error.
More information about this error may be available in the server error log.
Additionally, a 500 Internal Server Error error was encountered while trying to use an ErrorDocument to handle the request.`

The page I need help with: [log in to see the link]