Maybe worth removing everything from the motherboard and the battery too and leaving it for about an hour so all the components can fully empty of any power. Then reset the BIOS back to defaults using the jumper or if you can get into the BIOS through that. If you are not getting any video see if there is anyway of getting a speaker attached to the motherboard so you can hear the start up beeps as that will give you a big clue as to what is wrong.
I have played this game myself and it is really frustrating as you just don't know what the problem is. If you are getting a new CPU and motherboard I would try and not be tempted to test (if they are compatible) in the old setup as if there is something faulty it could fry the newly purchased component. I know you want to find out what the problem is but you may be better off not knowing. Where I used to work we had two £500,000 mainframe production printers. One wasn't working and the engineer who came to fix it started swapping parts between them. In the end we had two printers that didn't work because he fried components when he swapped them. After that we never allowed electronic part swapping unless. Mechanical parts was a bit different.
