Broken my wordpress site & domain setup

Hi there,

I have a domain. mydomain.co.uk which I have changed the DNS to point to my static IP address as I wish to host on my own server.

Ok I went into the wordpress settings on my webserver and changed WordPress address (URL) to mydomain.co.uk and now it doesnt allow me to enter the wordpress admin.

Can someone advise how to change it back to http://localhost/wordpress and then advise how to get mydomain.co.uk to point to my wordpress site.
I have forwarded port 80 to my webserver where the wordpress site is located.