x86 Program received signal SIGSEGV, Segmentation fault during debugging MASM32 assembly - debugging

Question

I am tasked with writing my first assembly code which takes a number between 1-12 entered by the user and outputs the factorial. I need to write 3 procedures one for the input, one to calculate factorial and one to print the result. I believe I have written it correctly (I didn't) but after getting the input from the user, the program terminates. I never see the result of my "Print" procedure. When trying to debug my code I get the error:
Program received signal SIGSEGV, Segmentation fault.
This error comes right after the first step of "invoke input"
Here is my complete code :
include c:\asmio\asm32.inc
includelib c:\asmio\asm32.lib
includelib c:\asmio\User32.lib ; SASM files for I/O
includelib c:\asmio\Kernel32.lib ; SASM files for I/O
input proto ; 0 parameters
Factorial proto nvx: dword ; 1 parameter
Print proto nax: dword, nf: dword ; 2 parameters
; -------------------------------------------------------
.const ; Section to declare and initialize constants
NULL = 0
; -------------------------------------------------------
.data ; Section to declare and initialize variables
nvx dword ?
nfx dword ?
nf dword ?
ask byte "Enter a number between 1-12: ", NULL
fin byte "! is ", NULL
; -------------------------------------------------------
.code ; The actual code begins here: Main program
main proc ; Just like C++ this is the main program
start:
invoke input
mov nvx, eax
invoke Factorial, nvx
mov nfx, eax
invoke Print, nvx, nfx
ret 0 ; need this line to return to caller
main endp ; End of the procedure main
; -------------------------------------------------------
input proc
mov edx, OFFSET ask
call WriteString
call ReadInt
ret
input endp
; -------------------------------------------------------
Factorial proc USES ECX EBX nv: dword
mov ecx, nv ;start loop counter at value given by user because we need to multiply this many times to find the factorial.
mov ebx, nv ; hold value of nv as divisor
inc nv ; This is to account for 0! We increment by one and after the loop divide by nv
mov eax, nv ; stores the largest number for multiplication
L1:
dec nv ; becomes next largest number
mul nv ; multiplication
mov eax, edx ; stores product into eax for next multiplication
loop L1
inc ebx
cdq
idiv ebx ; divide final product by original number + 1 for the correct factorial
ret
Factorial endp
Print proc nax: dword, na: dword
mov eax, nvx
call WriteString
mov eax, OFFSET fin
call WriteString
mov eax, na
call WriteString
ret
Print endp
end main ; End of the entire program
; -------------------------------------------------------