First thought--have you tried another hard drive? I've had Macs hang on that screen for a while if the drive is bad, yet not bad enough the Mac can't attempt to access them. This seems to be extremely common with MiniScribes in particular (I've had two in the past year alone do this to me). What kind of drive are you using?

Second thought--have you tried that drive in another Mac? This could narrow the problem down a bit, especially if you have an external drive to try (or any external SCSI drive; if you have the driver and can run it from a floppy it would be a good way to test). Note that an SE/30 can't boot from a CD.