Help needed to Write fist hello world operating system in pen drive.

I am not much knew to assembly language. I worked on it in my college days. But now i am again starting it after a gap of two years. Lot of things are gone. Except the interest in the simplicity in assembly language. Now i am trying to make a very small operating system of simply printing hello world. I am using pen drive in place of floppy here. the program i am using is
;----------------------------------------------------------------------
; Simple boot program that prints the letter 'H'
; and then hangs
; Joel Gompert 2001
;
; Disclaimer: I am not responsible for any results of the use of the contents
; of this file
;----------------------------------------------------------------------
org 0x7c ; This is where BIOS loads the bootloader


; Execution begins here
entry:
jmp short begin ; jump over the DOS boot record data


; ----------------------------------------------------------------------
; data portion of the "DOS BOOT RECORD"
; ----------------------------------------------------------------------
brINT13Flag DB 90H ; 0002h - 0EH for INT13 AH=42 READ
brOEM DB 'MSDOS5.0' ; 0003h - OEM name & DOS version (8 chars)
brBPS DW 512 ; 000Bh - Bytes/sector
brSPC DB 1 ; 000Dh - Sectors/cluster
brResCount DW 1 ; 000Eh - Reserved (boot) sectors
brFATs DB 2 ; 0010h - FAT copies
brRootEntries DW 0E0H ; 0011h - Root directory entries
brSectorCount DW 2880 ; 0013h - Sectors in volume, < 32MB
brMedia DB 240 ; 0015h - Media descriptor
brSPF DW 9 ; 0016h - Sectors per FAT
brSPH DW 18 ; 0018h - Sectors per track
brHPC DW 2 ; 001Ah - Number of Heads
brHidden DD 0 ; 001Ch - Hidden sectors
brSectors DD 0 ; 0020h - Total number of sectors
DB 0 ; 0024h - Physical drive no.
DB 0 ; 0025h - Reserved (FAT32)
DB 29H ; 0026h - Extended boot record sig
brSerialNum DD 404418EAH ; 0027h - Volume serial number (random)
brLabel DB 'Joels disk ' ; 002Bh - Volume label (11 chars)
brFSID DB 'FAT12 ' ; 0036h - File System ID (8 chars)
;------------------------------------------------------------------------


; --------------------------------------------
; Boot program code begins here
; --------------------------------------------
; boot code begins at 0x003E
begin:
mov ah, 0x0e ; Function to print a character to the screen
mov al, 'H' ; Which character to print
mov bl, 7 ; color/style to use for the character
int 0x10 ; print the character

hang:
jmp hang ; just loop forever.

;---------------------------------------------

size equ $ - entry
%if size+2 > 512
%error "code is too large for boot sector"
%endif
times (512 - size - 2) db 0

db 0x55, 0xAA ;2 byte boot signature

I save it in h.asm and then convert to bin file using nasm assembler by command
nasm c:\h.asm -fbin -o c:\h.bin

then i write it to my pendrive using debug by using the following commands
debug c:\h.bin
-l 0
-n f:\h.bin
-w 0


Now everything works uptill now.

When i reboot my pc making pen drive as priority boot device. Then i get the error
Error reading disk
Press any key to restart

Then i get message-
There is no boot data in your device.

Where the things are going wrong. Please help.

 

Firstly I'd like to Organize the code by using code tags and make it more readable..

Code:

;----------------------------------------------------------------------
; Simple boot program that prints the letter 'H'
;  and then hangs
; Joel Gompert 2001
;
; Disclaimer: I am not responsible for any results of the use of the contents
;   of this file
;----------------------------------------------------------------------
    org 0x7c    ; This is where BIOS loads the bootloader


; Execution begins here
entry:
    jmp short begin ; jump over the DOS boot record data


; ----------------------------------------------------------------------
; data portion of the "DOS BOOT RECORD"
; ----------------------------------------------------------------------
brINT13Flag     DB      90H             ; 0002h - 0EH for INT13 AH=42 READ
brOEM           DB      'MSDOS5.0'      ; 0003h - OEM name & DOS version (8 chars)
brBPS           DW      512             ; 000Bh - Bytes/sector
brSPC           DB      1               ; 000Dh - Sectors/cluster
brResCount      DW      1               ; 000Eh - Reserved (boot) sectors
brFATs          DB      2               ; 0010h - FAT copies
brRootEntries   DW      0E0H        ; 0011h - Root directory entries
brSectorCount   DW      2880        ; 0013h - Sectors in volume, < 32MB
brMedia         DB      240        ; 0015h - Media descriptor
brSPF           DW      9               ; 0016h - Sectors per FAT
brSPH           DW      18              ; 0018h - Sectors per track
brHPC           DW      2        ; 001Ah - Number of Heads
brHidden        DD      0               ; 001Ch - Hidden sectors
brSectors       DD      0            ; 0020h - Total number of sectors
        DB      0               ; 0024h - Physical drive no.
        DB      0               ; 0025h - Reserved (FAT32)
        DB      29H             ; 0026h - Extended boot record sig 
brSerialNum     DD      404418EAH       ; 0027h - Volume serial number (random)
brLabel         DB      'Joels disk '   ; 002Bh - Volume label  (11 chars)
brFSID          DB      'FAT12   '      ; 0036h - File System ID (8 chars)
;------------------------------------------------------------------------


; --------------------------------------------
;  Boot program code begins here
; --------------------------------------------
; boot code begins at 0x003E
begin:
    mov    ah, 0x0e    ; Function to print a character to the screen
    mov    al, 'H'        ; Which character to print
    mov    bl, 7        ; color/style to use for the character
    int    0x10        ; print the character

hang:
    jmp    hang        ; just loop forever.

;---------------------------------------------

size    equ    $ - entry
%if size+2 > 512
  %error "code is too large for boot sector"
%endif
    times    (512 - size - 2) db 0

    db    0x55, 0xAA        ;2  byte boot signature

And I have started Learning OS Boot Kernel and HERE is a very good code resource..