i would not let the phone flash a PD98IMG that you did not put there,its hard telling what it could be
are you sure the vol rocker isnt working? if you hold vol down,and power,from the phone being off(push vol down first),and it boots to a white screen with colored letters and checks a file,sounfs like its working fine- thats hboot. tell us the info on that screen.
i would put the card into a card reader,remove the PD98IMG that is prolly there on the sd. put the sd card back in,and boot to hboot again. for S&Gs,you might select recovery,and see if you go to "clockwork" or some other custom recovery,or a screen with a phone,triangle,and !(stock recovery)
you can try wiping cache/dalvik cache if you happen to get clockwork or custom recovery. with stock recovery,hold vol up intil you see a menu. then you can try the wipe cache option there as well.
failing that,boot to hboot,select fastboot with vol rocker/power. run the .exe as administrator(if your version of windows allows that) with the phone in this mode.
but,as iowa said,it would be good for you to tell us your hboot info first.that way we can better help you