Install to localhost

The downloaded/imported site still doesn't work.  But, it now displays a bunch of code/sql and ends with an error of "Fatal error: Class 'User' not found in C:\xampp\htdocs\system\core\Loader.php on line 303"

Is that a CodeIgniter application built under 2.x and now running under 3.x? I ask because CodeIgniter 3 has stricter capitalization rules.

And of course, gotta eliminate it as possibility -- the application does work "at home," where it was living before you took over?

Finally, like I say in my signature, get a debugger if possible. Netbeans and Codelobster both have one, and if you can get an older version of Notepad++, you can load the equally old an unsupported debug plugin. I have Notepad++ 6.5.5, and the debug plug in still works. It's a little unstable the more you use it, so I exit and restart Notepad++ from time to time.

Maybe I'm preaching to the choir, but it's invaluable to execute code line by line, see values change, and go, "Oh, there's where you're going wrong!"

Hey, don't work without a PHP debugger. Several free IDEs have this features built in. Two are NetBeans and CodeLobster. Without a debugger, it's like you're driving with a blindfold on -- you are going to crash!