problem in BIOS service

[MZeus]

I've written the following program

;print string using bios service
[org 0x0100]
                jmp start
message:        db      'hello world'

start:         mov ah, 0x13          ;service 13-printing string
                mov al, 1                ;subservice 01-update cursor
                mov bh, 0                ;output on page 0
                mov bl, 7                ;normal attribute
                mov dx, 0x0A03      ;row 10-column 3
                mov cx, 11            ;length of string
                push cs
                pop es                   ;segment of string
                mov bp, message    ;offset of string
                int 0x10                  ;call bios video services

                mov ax, 4c00h
                int 21h

when i try to run it on DOS an error is occured that
nasm: fatal: unable to open input file 'filename.asm'
kindly solve my problem.
thx

[Ancient Dragon]

my guess is that filename.asm is not in the directory where you are trying to assemble it. That, or you named the file something else.