Finder and Search failure

First post here, so be gentle with me...

I have a PPC G5, dual 1.8GHz which has become quite unstable, frequently crashing and requiring the use of Disk Utility and TechTool Deluxe. Usually these crashes are during a moment of high memory use like opening a vast Photoshop file or printing some multipage InDesign doc.

After one spectacular crash the HD wouldn't play ball, so I bought a new Hitachi SATA HD and whacked it in, fresh format, clean install of 10.4 from scratch, all Apps installed from disc then, once the old HD was recovered, copied back the user with Migration Assistant.

But my Mac still crashes.

Key to this, I suspect, is the fact that the Finder and Search facilities in 10.4.11 do not work. Specifically, if I use Spotlight or CMD+F to search for a file on my HDD, I get virtually no responses. Particularly Fonts will not show up and when I use the Search Entire Content facility in Mail, that too fails. Nothing.

So, has anyone had experience of Finder being unhelpful? Mail being difficult?

Any help or advice that doesn't involve a complete new installation would be received with boundless enthusiasm.

Good lord, I am inundated with a wealth of responses!!

This is pathetic, I logged onto a user group for Buell motorcycles and found an amiable and helpful bunch of people. I had rather expected a bit more from a Mac community. Hey **.