Hey guys,
I have a PowerBook 180 running Mac OS 7.5.5 with an intermittant booting problem. About 98% of the time when I start the machine up, all I get is the "missing disk" error symbol (question mark on a disk icon), as if it can't find the internal hard drive. I don't think it's a physical problem with the hard drive because of this: when I boot the machine with a bootable floppy disk (the one I usually use happens to be a OS 7.6 Disk Tools disk), it can see the hard drive fine and all the files on it. And here's the key -- when I soft restart from within the disk-booted OS 7.6, it ejects the disk, then proceeds to happily boot from OS 7.5.5 that is installed on the internal hard drive. Everything works fine until I power the machine down all the way, and upon attemping to boot again after that, I will get the "missing disk" error again.
This behavior makes me think that there is something wrong with the record on the HD that tells the Mac that it's bootable, however that works. I have a lot more experience in the DOS/Windows world and the best analogy I can think of is a corrupted Master Boot Record (MBR). I am not too familiar with the mechanics of classic Mac OS or its file system, so I'm not at all sure how to fix it. I am wondering if there is a way to restore this "boot record" on the internal hard drive without completely reinstalling the OS. Also, any explanation as to how Macintosh hard disk boot records work would be helpful. 
Any ideas? Thanks a ton in advance!
RedWolf
Basically, the Mac stores the Startup Disk info in the PRAM. I'm betting that the PRAM battery in your 180 is shot. It might even be causing the problem if it's so low it's corrupting PRAM info. When you power all the way off, are you also unplugging the power cord? Are you losing the time/date at powerup after being unplugged? If so, then the PRAM batt is certainly shot.
How long do you let it sit with the missing disk icon blinking? It might be scanning the SCSI bus for a bootable drive, and it might take it a minute to decide to go ahead and boot from the HDD.
Jon,
Thanks for your reply. I see now that the clock resets when I power the unit down and unplug it (the main battery is bad, of course, so that does the trick). So you're probably right about the PRAM battery being bad. I wonder how I go about replacing it.. need to figure out where it is. Hope I don't have to completely disassemble the unit!
Thanks again,
Red
The backup ('PRAM") battery in PB1xx Macs (certainly in the 160 and 180, with which I have been whiling away sanity recently) is a naked cell hard-soldered to the interconnect board beside the speaker. Apple's confidence in its longevity is usually justified. The 160 that I amalgamated with a 180 to make a passive-matrix 180 contributed, inter alia, its backup battery, which had been unused for five years in my hands, and for another six years in the former owner's. The assembled hybrid booted first go, keeps time and breathes deeply. However, your mileage could vary.
If Jon's suggestion profits you not, look rather more closely at the symbolism of the Quizzical Floppy. You have already gone close to the problem's cause, I suspect. QF says that the system cannot find a valid System Folder from which to load a System. There may not be one there. If, when booted from a floppy, you can see the mounted hard drive on the desktop, open the folder that represents it, then the System Folder, and find a System and Finder therein, this excuse is implausible.
The System may be corrupt. Since you can warm reboot from that same System on the hard drive, another excuse is knocked on the head.
The boot blocks may be pointing anywhere but at the 'blest' (valid) System Folder. Boot blocks? You fingered it. How do you withdraw from this doo-doo? Scorched-earth style, by reformat and re-install, is one way This will also make sure that the Apple partition system of the hard drive is refreshed/reconstructed.
There may be files on the hard drive that you wish to keep rather than blitz with a reformat, and which you cannot copy to safety beforehand. You may wish then to chance it by enlisting the aid of Alsoft's DiskWarrior, which, although it is a file directory rescue utility and not a hard drive repair utility as it is frequently misconstrued as being, will tizzy up the boot blocks after it has written a brand-new directory to the drive. DW 2.1.1 (old CDs, not those CDs on which it accompanies OS X), will boot your PB into System 7.6.1 (one of four bootable Systems/OSs on the CD) and allow DW to work its magic. Either an external CD-ROM, or SCSI Disk Mode from another ('host') Mac will enable this.
However, if the partition structure of the drive is at fault, only a reformat will give the drive new life, and a re-install give it a valid System Folder.
de