Q:

Conditional variables

I'm missing something, how do I make this work? 
var now = DateTime. Now;
string loadStartDate = Request. QueryString["sd"] == String. Empty ?  now. AddMonths( -14 ).ToShortDateString();
string loadEndDate = Request. QueryString[ "ed" ] == String. Empty ?  now. ToShortDateString();

Basically when the page loades if sd and/or ed is blank, then fill the date with my pre-defined stuff. 

A:

You are forgetting a : and the part after it. 
The conditional operator has three parts:

predicate (Request. QueryString["sd"] == String. Empty)
true branch
false branch

You are missing the false branch syntax and value. 
I would write it as:
string loadStartDate = string. IsNullOrWhitespace(Request. QueryString["sd"])
                       ?  now. AddMonths( -14 ).ToShortDateString()
                       : Request. QueryString["sd"];

Note:
string. IsNullOrWhitespace is new to .NET 4.0, so use string. IsNullOrEmpty for prior versions.