Well first i had a problem similar in which, the conversion to datetime was correct, but the month became the day.
Look at http://msdn.microsoft.com/en-us/library/9xk1h71t.aspx
] to see the culture format.
Second SELECT dat , product_id FROM market where dat >= YOUR_FIRST_DATE and ??? () you mush specify what do you want to compare.
Advise: look in the debug session and get the command that will be run, and run it in sql server(or what you use)