C# valid date

Question

In a C# 2008 application, I am obtaining a data from a web service via an xml file. In some instance a field is not a must not be a valid datetime value for a sql server 2008 r2 database.
Thus can you tell me:
 1. what check I can do to make certain the value is in a valid date time format?
 2. Also can you tell me how to convert the value to a valid datetime format?