“500 internal server error” when I altered my blog/word press URLs. Please help!

I finally managed to get my site up and running, with a couple of static pages. I finished my first blog post, but it wasn’t appearing on any of my pages. I started fiddling with the Settings to make my blog appear at philippajacks.co.uk/blog or philippajacks.co.uk/greenspaced but then it crashed and i can’t log into WordPress Admin or see my site or anything!

This is the error I’m getting:

“Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator, [email protected] and inform them of the time the error occurred, and anything you might have done that may have caused the 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.”

Does anyone have any idea what I can do? I was doing so well, and now I’m gutted!