Project Euler Problem 3 Solution with C#

ProjectEuler.P3.cs

using System;
using System.Collections.Generic;
using System.Text;

namespace ConsolesTests
{
    class Program
    {
        static void Main(string[] args)
        {
            long NUM = 600851475143;
            long LargestPrime = 0;
           // NUM = (long)Math.Sqrt(NUM);
            for (long i = 2; i*i < NUM; i++)
            {
                if (IsFactorOf(NUM, i))
                    if (IsPrime(i))
                    {
                        Console.WriteLine(i + " : is prime & is factor ");
                        if (i > LargestPrime)
                            LargestPrime = i;
                    }
            }
            Console.WriteLine("\n Done.... and the Largest Prime Factor is : " +LargestPrime);
        }
        
        static bool IsPrime(long x) {
            for (int i = 2; i < x;++i )
                if (x % i == 0)
                    return false;
            return true;
        }
        
        static bool IsFactorOf(long x, long y)
        {
            if (x % y == 0)
                return true;
            return false;
        }
    }
}

oh, i think this solution will take tooo much time doesn't it ? i tried this before and solution took about half an our on a code2due processor if i remember.