Dell XPS One 2720 AIO Black Screen

[Seagorman]

Hi Guys, I have a Dell XPS One 2720 AIO with a strange problem, more often than not when i boot up i get a totally black screen, no Dell splash screen, i have discovered that if the PC is left on for approximately 20 mins or so and i press the Keyboard or Mouse the login screen appears and the PC works fine until turned off again, I suspect that the problem may be related to the onboard nVidia graphic chip. I have tested the Ram out of system and its fine, i have tried booting with H/D, DVD disconnected, no luck, I have removed the CMOS battery and left the system sitting unplugged over night, shorted the CMOS battery contacts and even tried a new CMOS battery, same thing. most recently i tried a reflow on the graphic chip without success, PSU has also been tested. If the problem was due to faulty Graphic chip would it still work OK the way it is now when it eventually comes on, is there a possibility some other component could be the culprit, a visual inspection of the Mobo + its daughter boards all look perfectly normal, almost all caps are metal type. I can put the PC into sleep mode instead of shutting down and all is grand but if reboot is required at any stage after updates or installing new software i'm back to the black screen issue again, any thoughts or recommendations would be most thankful, many thanks in advance guys.