I have a suggestion that wont cost much to try, before you start buying parts. Several years ago, i inherited an old packard bell with a slot 1 board, that had similar problems. The guy that owned it was a very heavy smoker, and a computer guru, but he couldnt get this one to work. When i took the cover off, it was like an ash tray inside, with brown residue from the smoke in, and on everything. I took all the cards out, and cleaned all the contacts, took the cpu out cleaned it and the socket. I cleaned the slots on the motherboard, by finding a piece of cardboard from a shoebox, that just fit between the contacts. Dipped it in cleaner, and pushed it in and out of the slots, till they were clean. Then sprayed everything down with cleaner, and let it dry good. The tar ran off in sheets. I put it back together, and its still running today. This is not to say that smoke is your problem, but it could be dirty contacts. I use "Brakleen" by CRC, as a cleaner, because i cant always get contact cleaner here. It works great, drys fast, and doesnt leave a residue. Like most contact cleaners though, it will attack some plastics, rubbers, and paint.
If you have to buy parts though, ebay has tons of slot 1 stuff. They even have adapters to run different cpu`s on the slot 1 boards, but you shouldnt have any trouble finding cpu`s, or mb`s.

Thanks for the thoughts, Uncleed.
Makes me wish this computer was gunky! It might give me a chance... But it was as clean as ever you could wish - almost 100% dust-free - incredible really.
Connections all seem tight but - maybe... I'll have to investigate the chip in its elaborate block housing - no idea as yet how its fixed in - I guess I'll have a look and go by what seems logical.... so I can try the spray job - not much to lose, I guess!

If I have to go to replacements - Do you - or anyone else - know if in this case the L2 cache is part of the chip, or outside? If it is onboard, is it an idea to try to get a substitute chip, rather than a motherboard?

Continued thanks to all who give me their experience / expertise!

Hi grayman...
L2 cache is part of the CPU and can't be "replaced".

If you need to replace parts, I'd suggest comparing the price of the replacement parts with that of a new computer...it may work out to be worth your while - but I do understand that upgrading for some people is not an option

Heres something else i forgot to mention, that battery is probably going on 7 or 8 years old, or more. You might check the voltage, or just replace it. Some of your symptoms could be related to that. Check your bios settings before you take it out, so you can set it back like it is, and tweak from there. But i agree with GaRHaR, i wouldnt spend a whole bunch on it. Even if you upgraded the cpu while youre fixing it, that board may not support one much faster.

Thanks GaRhaR, thanks uncleed.
If I look for a replacement 'puter I must try to find something a bit old - a) for price and b) for compatibility with this sound card! [which is why I bought this baby...;-) ]
Good thought about the battery, uncleed - I'll have a look later when I get time - and note down the config first! This board has a jumper to reset the bios anyway - I guess it would be a test of some kind to do that and try an install in any case. Any ideas if generally one can download bios settings to disk or if things are noted manually?