Mini died, had to reinstall OS X. Want to know what happened.

Question

I'm pretty sure that this is a Tiger problem, not a Mini problem. First, I'll give a short version, then a longer version for anybody who's interested.
SHORT VERSION: I was reading a web page with my Mac Mini, OS 10.4.11, using Firefox. The mouse cursor suddenly vanished, the keyboard wouldn't respond, not even command/opt/esc. After power cycling, I could not even log in. I tried every troubleshooting tip I could find in the Mini manual, and Mac Help on my MacBook. Details below, but nothing worked. I was able to start it in target disk mode. I used my MacBook to transfer essential files from the Mini to an external hard drive. Then I reinstalled OS 10.4.6 using Archive and install, and upgraded it to 10.4.11 again. Most things are working again; occasionally I run into a problem with a specific program and have to reinstall or re-configure. I'm using the Mini to type this.
I still want to understand what could have happened to cause this sudden crash. Probably "some kind of file corruption", but what could have made that happen, and happen so suddenly?
LONG VERSION: First, a little history. I've been getting little freezes on this computer for a couple of months now. Up to now, I've been able to unfreeze it by going into sleep mode (holding down power button for only a couple of seconds) and waking it up again. I have run Disk Utility verify and repair about once a month. It usually seems to find some inconsistencies in file names, hazy on details, and "repairs" them. Have not run fsck. I have been using the MacJanitor daily, weekly, and monthly checks; I know these can just be run from the command line too.
So the computer crashed as described above. The first time I tried to restart it (by power-cycling), it got to a login screen after about ten minutes, then froze for about twenty minutes before I got impatient and power-cycled it again. After that, it never even made it as far as the login screen. Every time, I gave it at least ten minutes to think it over.
I tried Mac safe mode, and gave that about twenty minutes to do something. It never got beyond the gray screen with the spinning progress disk.
As mentioned above, I opened it as a target disk, and used my laptop to backup files to a separate hard drive.
I knew that you could boot up from an install disk, but I missed the Mac help suggestion of running first aid from that disk until after I'd reinstalled the OS. So I missed a bet there, but I don't know if it would have clued me in to what had actually happened.
As mentioned earlier, I did an archive and install. I'm wondering if there might be some log files somewhere still on my hard drive that would give a clue as to what went wrong. Not really sure where, or for what, to look.
This whole sudden death thing has been very disturbing. I've had this computer for two years, and I'd like to be able to get at least another two out of it if I choose. I don't expect any OS to be perfect, but this shakes my faith in OS X a bit.
Rare though Mac viruses are, it occurred to me that I might be one of the rare unlucky ones. Since I didn't do a completely fresh install, if it were that, it could still be there. My Norton subscription expired, and it's been uninstalled. I've been using ClamX on the MacBook, but it won't scan the whole hard drive, you have to know where to look. So if I put ClamX, on the Mini, where would be a likely place to look for a virus?
I'm assuming that this was an OS rather than a hardware problem just because it was possible to restore, and everything is working again for now. System profiler seems to show all the hardware as it should be. If there are holes in that logic, it would be helpful to know.
I think that's about it. Thanks in advance to anyone with the patience to read through this mess.

Answer 1

A lot of things can cause corruption in disk directory data. And it can be a hardware problem with the hard drive, such as bad sectors. It can be caused if the computer ever lost power suddenly, like in a power outage, while it was writing data to the drive.
I still want to understand what could have happened to cause this sudden crash
As you said yourself, it was not actually "sudden." You were getting "little freezes" for a few months which progressively worsened.
Doing an +Archive and Install+ may not fix the problem, if Disk Utility still reports the problem when you do a +Repair Disk+ (while started up from another disk such as your installation disk). If it does not report the problem anymore, the problem was probably fixed.
A good way to stress test your hard drive and get rid of the problem (if it still exists), is to backup your personal data and erase the drive. But when you use Disk Utility to Erase (reformat) the drive, select the +Security Option+ to +zero out data+. This writes zeros to every sector. Bad sectors (if any) will be mapped out. If the hard drive has too many bad sectors or some other problem, this procedure will fail. Doing the +zero out data+ process takes time.
If it completes successfully, you should reinstall Mac OS X and your apps, and then restore your personal data.