Change Password

I cant change the password when dialing a dialup service,
the dialog box comes up with a same long password, one
that i never enter, but its always there, then i click on
settings and change the password, but when i click ok,
and go back to the dialup box, its the same long
password, i closed the box and tried many time, but dont
work, ive been trying to check all my passwords stored in
windows, but i dont see that long password, can anyone
help???