Print Number After using div and mod -not working MASM

I'm trying to write a program that get a String that contains number, and put in Sum2 variable the sum of the digits of the number that the function got. this is what I wrote but It doesn't work and I don't know why:

.386 
.MODEL Flat, STDCALL 
option casemap:none 

SomeFunc proto :DWORD

include \masm32\include\windows.inc
include \masm32\include\msvcrt.inc
includelib \masm32\lib\msvcrt.lib

.data

    Sum2 dd ?
    stop db 0
    fmt db '%s',0

.code

SomeFunc proc Number:DWORD
    Lop:
        mov eax,Number
        mov ebx,'10'
        xor edx,edx
        div ebx
        add Sum2,edx
        mov Number,eax
        cmp Number,0
        jna Lop
    ret
SomeFunc endp

start:
    invoke SomeFunc,'123'
    invoke crt_printf,offset Sum2,offset fmt
end start

I really don't understand why it doesn't work and how do I make it work. can someone explain me? Sorry for my bad english. thanks for the help.

Solution

Concentrating on SomeFunc

You should clear Sum2 before using this function. Without doing so you can only hope to be lucky 1 time.
You want to divide by 10 and not by a string '10'
You need to continue the loop for as long as EAX is not zero.

Applying all of this gives:

SomeFunc proc Number:DWORD
  mov Sum2, 0
  mov eax, Number
  mov ebx, 10
 Lop:
  xor edx, edx
  div ebx
  add Sum2, edx
  mov Number, eax
  cmp eax, 0
  jne Lop
  ret
SomeFunc endp

Do note that SomeFunc expects a number whereas invoke SomeFunc,'123' passes a pointer to a 3-character string.