Resurrecting an old computer (perhaps)

Today I didn't feel like doing anything I should be doing, so I looked on my low-priority list and found "see if the old desktop computer works". I bought this machine in late 2001 and it went through 2 main boards in rapid succession and then (after the warranty had expired) developed more faults, like refusing to start -- an apparent hardware problem. I speculated that it might be heat-and-humidity related, since I've mostly attempted to use it during the summer. Today I tried to start it and it booted up and ran for a few hours before quitting. I booted it again, with the same result. I then took the sides off so I can see whether the CPU fan is failing, or something else semi-obvious is happening -- it failed again while I was out taking my evening walk, but the CPU fan was still going fine. Tomorrow I start pulling out boards and doing other boring diagnostic stuff. Whether we get it working or not, it's going out -- either to a good home (preferably in a drier climate) or to someone to use for spare parts. I suspect that in a less humid climate, it would run fine. A former neighbour had an old computer that gave her endless trouble while she lived here, but after she moved to Canberra (which has a very dry climate) two years ago, her computer worked perfectly.