ntvdm encountered a hard error

Hi all. While writing a boot sector reader, I encountered this error:
NTVDM encountered a hard error. That occurs when i call the int 13h
with these parameters:

ah=02h
al=1 ;how many sectors?
ch=0 ;cylinder
cl=0 ;sector to read
dh=0 ;head
dl=80h ;first hard drive
es:bx => buffer 512 bytes long

if I read a floppy drive (dl=0), than everything goes right, but I
cannot read a hd. What is wrong? I'm using windows vista rc1 (but I
don't think it's a beta system bug)
thx everybody

.