I want to get all the list of week

The way you're doing the week number caculation is wrong as Vivek[^] already pointed out in his answer the correct way to do this is to use Calendar.GetWeekOfYear. In my example below I used the GregorianCalendar with GregorianCalendarType.Localized. For the method GetWeekOfYear to work correctly though you will have to use CalendarWeekRule to specify how a week is started when transitioning from one year to the next. Equally important is how the first DayOfWeek is defined in your locale. In my country Monday is the correct day, but that may differ where you are.
Depending on the value of CalendarWeekRule there are different results to be obtained. Weeks may either span across a year boundary or my have less than 7 days. The following list exlains how this value can be used to define the behavior:

1. FirstDay: Indicates that the first week of the year starts on the first day of the year and ends before the following designated first day of the week. The value is 0. This value ensures that a week does not span two years.
2. FirstFullWeek: Indicates that the first week of the year begins on the first occurrence of the designated first day of the week on or after the first day of the year. The value is 1. This value will make sure that there will never be any odd weeks in the list of calculated weeks, but a week may span across the year boundary.
3. FirstFourDayWeek: Indicates that the first week of the year is the first week with four or more days before the designated first day of the week. The value is 2.

Disclaimer!: The following code is is in C# and not in VB.net. My proficiency in VB.net not good so I used the language I usually code in. I hope you'll be able to understand what I did. If you have any specific question about parts of the code you don't understand, I'll be happy to try to explain it to you. Not using VB.net has nothing to do with a like or dislike of that language.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Globalization;
namespace WeekCount
{
    class Program
    {
        static void Main(string[] args)
        {
            DateTime start = new DateTime(2010, 1, 1);
            DateTime end = new DateTime(2010, 12, 31);
            DateTime current = start;
            GregorianCalendar calendar = new GregorianCalendar(GregorianCalendarTypes.Localized);
            CalendarWeekRule rule = CalendarWeekRule.FirstDay;
            DayOfWeek firstDayOfWeek = DayOfWeek.Monday;
            List<Week> weeks = Week.GetAllWeeks(
                start,
                end,
                rule,
                firstDayOfWeek,
                GregorianCalendarTypes.Localized);

            // This block will filter the weeks list so only weeks with a odd number of days
            // will be output
            List<Week> oddWeeks = weeks.FindAll(delegate(Week week)
            {
                return week.IsOdd;
            });
            int total = weeks.Count;
            String verb1 = total > 1 ? "are a total of" : "is";
            String plural1 = total > 1 ? "s" : "";
            int odd = oddWeeks.Count;
            String verb2   = odd > 1 || odd == 0 ? "are" : "is an";
            String plural2 = odd > 1 || odd == 0 ? "s" : "";
            String formatStatistics = "There {0} {1} week{2} in the list of which {3} {4} odd week{5}.\n";
            Console.WriteLine(formatStatistics,
                new Object[] {verb1, total, plural1, odd, verb2, plural2});
            String formatLoop = "Start: {0:ddd MMM dd.} End: {1:ddd MMM dd.} Number: {2:00} Days: {3:00} Year: {4:####}";
            foreach (Week week in oddWeeks)
            {
                Console.WriteLine(formatLoop, new Object[] {
                    week.Start,
                    week.End,
                    week.Number,
                    week.Days,
                    week.Year}
                );
            }
            Console.ReadLine();
        }
    }
    public class Week
    {
        public DateTime Start { get; set; }                                 // Start date of the week
        public DateTime End { get; set; }                                   // End date of the week
        public int Number { get; set; }                                     // Number of week
        public int Days { get { return End.Subtract(Start).Days + 1; } }    // How many days does the week have
        public bool IsOdd { get { return Days < 7; } }                   // A week is odd if it has less than 7 days
        public int Year { get { return Start.Year; } }                      // Which year does this week belong to

        public Week(DateTime start, DateTime end, int weekNumber)
        {
            this.Start  = new DateTime(start.Year, start.Month, start.Day);
            this.End    = new DateTime(end.Year, end.Month, end.Day);
            this.Number = weekNumber;
        }


        public bool Contains(DateTime date)
        {
            DateTime tmp = new DateTime(date.Year, date.Month, date.Day);
            return Start <= tmp && tmp <= End;
        }


        public static List<Week> GetAllWeeks(
            DateTime start,
            DateTime end,
            CalendarWeekRule rule,
            DayOfWeek firstDayOfWeek,
            GregorianCalendarTypes calendarType)
        {
            GregorianCalendar calendar = new GregorianCalendar(calendarType);
            List<Week> result = new List<Week>();
            DateTime currentDate = start;
            // Find start date of current week of year
            int currentWeekNumber = calendar.GetWeekOfYear(currentDate, rule, firstDayOfWeek);
            do
            {
                currentDate = currentDate.AddDays(-1);
            } while (currentWeekNumber == calendar.GetWeekOfYear(currentDate, rule, firstDayOfWeek));
            currentDate = currentDate.AddDays(1);
            Week currentWeek = null;
            DateTime startDateOfWeek = currentDate;
            int nextWeekNumber = currentWeekNumber;
            while (currentDate < end)
            {
                currentDate = currentDate.AddDays(1);
                if (currentWeekNumber != calendar.GetWeekOfYear(currentDate, rule, firstDayOfWeek))
                {
                    currentWeek = new Week(startDateOfWeek, currentDate.AddDays(-1), currentWeekNumber);
                    result.Add(currentWeek);
                    currentWeekNumber = calendar.GetWeekOfYear(currentDate, rule, firstDayOfWeek);
                    startDateOfWeek = currentDate;
                }
            }
            // We need to add another week if none are in the result or if we have a startDateOfWeek
            // different from our last result
            if (result.Count == 0 || startDateOfWeek != result.Last().Start)
            {
                // Now lets seek to the end of the week
                while (currentWeekNumber == calendar.GetWeekOfYear(currentDate, rule, firstDayOfWeek))
                {
                    currentDate = currentDate.AddDays(1);
                }
                result.Add(new Week(startDateOfWeek, currentDate.AddDays(-1), currentWeekNumber));
            }
            return result;
        }
    }
}

Dim dateFrom As New DateTime(2006, 7, 1)
        Dim dateTo As New DateTime(2011, 12, 31)
        ' Difference in days, hours, and minutes.
        'NumberOfWeeks(oldDate, newDate)
        Dim Span As TimeSpan = dateTo.Subtract(dateFrom)
        If Span.Days <= 7 Then
            If dateFrom.DayOfWeek > dateTo.DayOfWeek Then
            End If

        End If
        Dim Days As Integer = Span.Days - 7 + CInt(dateFrom.DayOfWeek)
        Dim WeekCount As Integer = 1
        Dim DayCount As Integer = 0
        WeekCount = 1
        While DayCount < Days
            DayCount =DayCount + 7
            WeekCount = WeekCount + 1
        End While
        drpWeeknos.Items.Add(WeekCount)

Try dis..........