I have followed the installation instructions for a local machine (on a windows 7 machine) for the purpose of testing (LimeSurvey version on date 2014-05-02).
After completion, the '/admin' URL opened as a 404 page. When I checked the XAMPP Control Panel the Apache was not running. After changing the port from 80 to 8080, Apache now ran and the 404 issue was removed, however I am now getting this error;

Internal Server Error

CDbConnection failed to open the DB connection

Does anybody have any idea what may be the cause/solution?

What the error message said. Limesurvey couldn't get a connection to the database.

What database are you using? If you using the mysql it might be the case that the database isn't runnung. Just like Apache wasn't running in the first place on your PC.

If you unused to XAMPP please consult the forum of the project
community.apachefriends.org/f/viewforum.php?f=16

Infos about XAMPP and Limesurvey:
www.limesurvey.org/manual/Installation_o...Survey_XAMPP_package

You may have a look at this previous post