Hardware or software?

Question

I'd appreciate some views about whether my totally flaky PowerBook is suffering from hardware or software problems, if it's possible to tell.
The computer goes bad in various ways but most frequently some application will stop responding, and soon after that nothing can be saved, error messages appear about disk problems or shared library problems, and so on. Restarting would usually restore everything for a while, but it's been getting worse. This trouble started after I had a new (Apple) hard drive installed, but the place that installed it has twice checked the drive and all my hardware, and all tests were passed.
When the trouble grew constant, I wiped my drive clean, installed a new system, dragged in the contents of folders from a backup, and things were better for a while and then got just as bad and even worse.
What I did next makes me think that it's a hardware problem, like perhaps the new drive or RAM (both under warranty), and I'd like to know whether this makes sense:
My backup is on an external HD, created with Carbon Copy Cloner. I can boot from that backup and everything functions normally-- I don't think I've ever had a problem when booted from the external system. But recently I (again)reformatted my laptop's drive and used CCC to clone from the external to the internal drive, and the resulting system would start up and immediately be frozen. Does it follow from this that either my cloning was imperfect or there is a hardware problem on my laptop?
(I then reformatted the drive again, installed a fresh system and used Migration Assistant, or whatever it's called, to pull in the contents of my backup, and it worked for about a week and then got even flakier than ever. Won't boot up at all anymore. The bootable backup still seems fine, though.)
The place that replaced my HD say the computer is old, just get a new one. But if it's just the drive, or just the RAM...

Answer 1

After about a day and a half with the new hard drive installed, I have yet to see any evidence of my recurring problems. I spent the first evening using only a newly installed system on the new drive (worked fine), then yesterday morning I cloned everything back from my external "backup". So it's been a day of apparent full functioning. Considering that in its last stages, my computer wasn't able to even open Safari, this does point to a bad hard drive. The only other possibility, I suppose, could be some sort of loose connection that had gotten progressively worse, which could have jiggled back into place during the drive swap, in which case it might show itself again gradually as it did before (the problems started a few weeks after the HD was installed). At any rate, I seem to have a working computer at the moment, which is only to the good.
After another day or so I am going to try to open Eudora. This was what seemed to trigger all of my earlier problems (they first began shortly after I made a change in Eudora Preferences, and the HD installers assured me that the problem was not in their new drive and that my "Eudora was toast." After that, it did seem that every time I used Eudora, problems would arise (rebooting seemed to make them okay temporarily) and so I have not used my POP3 email for months, and have about a thousand emails up on the server that will download into Eudora In as soon as I dare to try this.
The guy who installed (in May) the almost-surely-bad HD said that if my experiment proved the drive was bad, I would probably be out of luck because the warranty on that drive had run out, which is a laugh because I came back with a complaint, for the first of about four times, only three weeks after it had been put in. But I don't know if it's worthwhile pursuing justice (assuming my new new drive continues to work). As I said, I do not need another 80GB drive, and don't think I ever will. Should I try to demand a refund for that drive and the labor costs of installing it and transfering data?
Message was edited by: Paul-ny