Site has gone down

I don’t know what happened but my wordpress site has gone completely.

I cannot even access the wp-admin login area anymore.

I’ve contacted 123 reg but they say the hosting is fine and everything is OK their end. They aren’t helping at all and say they cant do anything to help. They say I need to check the website itself -but I can’t do this because I can’t log into it

it says yourhealthmate.co.uk is currently unable to handle this request.
HTTP ERROR 500

http://yourhealthmate.co.uk/

They say it is a coding issue in the website – but I built this myself and haven’t been into the dashboard for a good while – and I haven’t changed anything different since it was working so I have no clue what to do.

And as I say, I can’t even get the log-in page up – it has the same error 500 thing.

Any help or suggestions would be most appreciated.