Non Repeating Random Number Generator

Hello Everyone,

First off, thanks for looking at this post. I'm relatively new to coding in VBA and am starting to get a little bit of it. But, I have this random number generator (I didn't code it) that I've been using. Unfortunately, it's been crashing when I've been trying to modify it. I think the chance of it crashing increases as the range of random numbers decrease in proportion to the amount of numbers you want to generate increases.

In any event, here's what I would like the code to do:
1. List numbers 1-50
2. List all 50 numbers random
3. No repeats.

Below is the code:

Option Explicit

Sub Random()
    Dim x As Long, y As Long, z As Long, tempnum As Long
    Dim flag As Boolean
    Dim i As Integer
    Dim foundCell As Range
    Application.ScreenUpdating = False
    x = Application.InputBox("Enter starting Random Number", "Random Number Generation", 1, , , , , 1)
    y = Application.InputBox("Enter ending Random Number", "Random Number Generation", 1000, , , , , 1)
    z = Application.InputBox("How many random numbers would" & "you like to generate (<15000)?", "Random Number Generation", 100, , , , , 1)
    If z = 0 Then Exit Sub
    If z > 15000 Then z = 15000
    If z > y - x + 1 Then
        MsgBox "You specified more numbers to return than " & "are possible in the range!"
        Exit Sub
    End If
    Randomize
    Cells(1, 1) = Int((y - x + 1) * Rnd + x)
    For i = 2 To z
        Do
            flag = False
            Randomize
            tempnum = Int((y - x + 1) * Rnd + x)
            Set foundCell = Range("a1", Range("a1").End(xlDown).Address).Find(tempnum)
            If Not (foundCell Is Nothing) Then
                flag = True
            End If
        Loop Until Not flag
        Cells(i, 1) = tempnum
    Next
End Sub