HP DV5000 keeps shutting off after replacing almost everything

It first happened a few years ago and replacing the heatsink fixed it. This time new heatsink n fan did not work, then replaced cpu w refurb and still shutting off, then replaced motherboard w refurb and a little better but still shuts off before i can even install an OS. Removed memory and tried one at a time but no change. Any help would be appreciated