what up lewis. . .
has this 638 ever booted up normally?
which os are you running?
do you have other macs?
do you have any external scsi drives?
do you have any OSs on CD?
I can't say much, but usually, if I get this (has happened once on an overclocked Q610), I use an external disk as the boot device. If this boots, then you can rule out a few things. If you answer the above questions, we might be abe to help you further.
I have a problem with vintage electronics. . .I am working on it.
Performa 630CD,Performa637CD,Centris 610,Quadra 630,Quadra 950,Quadra 605,SE,8500/180,G3,Giant 80mb SCSI HD,Giant 100mb SCSI HD