You should invest into a POST card. With this, you could know if there is any activity left in the board. This won't tell you what's the problem, but it will probably help. For example, if your motherboard doesn't output any code, either the CPU is dead, or something on the board itself is dead. But even if there's a code, that doesn't mean that it will be repairable either 😒
This helped me to find out that a socket 3 board was completely dead (working CPU and no POST code) and that one of my socket 7 board had a dead bios rom (there was a code, but it was the only one the board could output so that meant that there was still some activity in that board. I've got a slot 1 board that doesn't start up, but I know that it might be repairable too because there is really some activity there. But I don't feel the need of repairing it right now because I've got 2 other spare slot 1 boards that are working properly and are also less limited than this packard bell board