OK so after further testing of the machine I figured the issue out It appears to be the (dell chassis intrusion switch) i’m guessing this malfunctioned somehow.  further testing 100% confirms this as the issue  [NAME] [NAME]     
So... My dell is not 100% stock. I do have a 16 GB of RAM and a GTX 1060 in here  before I did this upgrades obviously I had to upgrade the power supply because it wasn’t enough to handle the graphics card so I got a new PSU  The computer worked fine for about three months then I experienced a random shut down didn’t think anything of it just thought it over heated... then it did it again the next day  I opened up the Computer and reseated  everything. I go to plug it in and it doesn’t turn on the only signs of power or the amber light on the motherboard (((no other lights))). Eventually after messing around with stuff he does eventually turn on.  it’s just starting to annoy me now is there any fix to this because I have so far seen nothing on this issue besides an old article from 2014    help is much appreciated thanks -Sam   
Dell OptiPlex 390 Random shutdowns and refusal to turn on after unplugging