Mine belonged to my father in law. It’s a Lenovo Think Centre M58 dead in the water. I went through all the diagnostic advice and determined the power supply was out. I hooked another power supply and unit booted up. I tore the PS down and found several swollen electrolytic capacitors on the PS board. After replacing them the system booted right up.
I replaced my battery and ended up with the same trouble. Later, replacing the front camera assembly fixed my phone. The ribbon ripped in the sharp turn, apparently when I initially opened the phone. Thanks for all the input.