NEWS5000SB POST failure

Dear users of SONY NEWS,

  My NEWS5000SB does not boot. Please help me.

  I tried to boot NEWS5000SB for the first time in 14-15 years. But 
NEWS5000SB did not boot.
  I tried the following:

1.when I connect the power cable and push the power button, 
  NEWS5000SB starts up and the fans also turn, but there is a 
  noise from the fans and nothing is displayed on the screen. Also
  "NETWORK" LED on front panel flashes rapidly
2.I disassemble NEWS5000SB, cleaned up and confirmed the 
  condition, but I cannot find a problem, such as burning of IC, 
  rupture of condenser, and so on
3.I reassembled and connect the power cable, but I do not insert 
  memories
4.when I push the power button, but the result is the same as 1
5.I turned off DIP switch #1 and #2, this means using serial 
  console
6.I connect the serial cable, and push the power button, but 
  nothing is displayed on the serial console(TeraTerm on 
  Windows10)
7.I confirmed that the all fan's cable is 2 pins. Therefore, it 
  seems that NEWS5000SB has not detected the rotation of the 
  fan

  I think that flashing of "NETWORK" LED signifies failure of 
POST. So, I think that if I recognize why POST fails, I might 
understand how to deal with it.
  Does anyone know how to display the progress of POST on 
the NEWS5000 series?

Best regards,
-- 
Yoshihiko Iwama