running an ibook g3 500mhz 192ram

i was editing my yaboot.conf so i could try to get my brightness keys working..

now i'm getting
/pci@f4000000/ata-6@d/disk@0:3, \\hda3: unable to open file, invalid device
when i rebooted

this wasnt the original entry in my yaboot.conf, but I cant remember what the original is and I don't have a bootable cd. i do have a backup of yaboot called yaboot.conf.bak but i dont know how i can access it. i'm stuck at the 2nd stage boot menu.

help please