OK - - - I have a notable power on problem with a Dell XPS8900.

Symptoms: 

* Start button appears to do nothing in all cases.

* Upon connecting power, the computer will "attempt" a power up, fans spin, and about 1 second later everything dies. Upon waiting a period of time (minutes), I get the same result.  If I DON'T wait, and reconnect power immediately. . . nothing happens.   Note that the power up attempt is happening WITHOUT touching the start button. 

* If I remove the CMOS battery and wait a while (minutes), and then install the battery and then power the following happens;   The computer does the "power up attempt" three - four times in short succession. On the third or fourth attempt, the PC boots up.  I do get a BIOS error for lost clock setting.  It **Seems** like the PC is struggling to get data off the hard disk (it is a HDD), and firing up Windows seems to take more time than it used to. Note: Start button is not pressed in this scenario.  

* After cycling the installation of the CMOS battery and getting a boot up, I can restart through windows. If I shutdown through windows, and come back to the computer 60 seconds later, it won't boot up (same behavior as noted above).  

Troubleshooting to date:

* Replaced the power supply (yikers. . . )(no change in performance)

* Replaced the CMOS battery (first with one from another device, then with a fresh one purchased today) (no change in performance) 

* No errors in device manager; HDD and optical disk is accessible (HDD seems slow). No memory error.  The video card (GTX1060) seems to be alive. Once running, the computer seems "normal".

Any thoughts?  (Yes. . .I have now recovered all necessary data off the machine. . . so I can be brave with experimentation)