Here you will see how to find Start and End date for a specified date in ASP.Net.
Just use these functions...
DateTime lFnGetBeginningOfWeek(DateTime date)
{
return date.AddDays(-1 * (int)date.DayOfWeek).Date;
}
DateTime lFnGetEndOfWeek(DateTime aDate)
return aDate.AddDays(6 - (int)aDate.DayOfWeek);