a) You can boot it from a bootable floppy, and reformat the internal HD from there. System 7.1.1 was what it was born with (and it required an “enabler” file) but 7.5, more readily obtainable, ought to boot that sucker right up. More to the point, perhaps, you may be able to boot from floppy and access the files that are on the hard disk before reformatting, using tools such as DeskZap.
b) You should also be able to boot from an external SCSI device such as a Zip drive, SyQuest drive, external hard drive, etc. It will need to be HFS formatted (not HFS+) and have an OS version somewhere between 7.1.1 + PB 150 enabler and MacOS 7.6.1; to tell the PB to boot from the external device by default, you may have to hold down Command-Option-Delete-Shift until you see the smiling Mac face and the parade of extension icons. Again, you can reformat from there and/or try to access the files on the internal HD using various utility tools.
If you can edit the fies on the internal HD with a tool such as DeskZap, you may be able to trash whatever preferences or extensions are locking the HD at boot. I don’t think it was anything stored in parameter RAM, just plain files that load at boot time off the hard drive. Not even sure if you need utilities at all if you boot from something other than the internal HD, you might have full access via the Finder and just toss out the extension or control panel that does the security, such as it is. (I could be wrong about that, but I don’t remember much in the way of serious security measured in those days on the Mac)