Error in system registery

My other computer running windows xp has some kind of
system registery error and wont boot to windows xp.. ive
tried everything to fix it.. when i try to use recovery
console, it asks me for the administrative password,
which im pretty sure never set and left blank, and it
wont accept the password as blank. When i try to use
repair by using the disk i used to install windows xp, it
fails to find the instalation of windows xp on the hard
drive which is surprising. I cant install it again since
all 4 of my drives have under 1gb of memory needed for
win xp. Help me please.. i cant get it to start at all.