XPS 18 1820 Won't POST - Power LED 7 white blinks

Hi,

I rebooted my XPS 18 after a Windows 10 update (I think it did the graphics drivers) and now it won't boot.

No logo, no POST... nada.  Holding the power button down for around 10 seconds, I can here a subtle click and whir, which I think is the HD and CPU fan shutting off.  Then hitting power button again, I see a blink code on the power LED: 7 white blinks, pause, repeat.

I cant get past this.  Plugging in a USB keyboard and hitting F12 does nothing. 

No difference between powering the stand and plugging power cord in directly.

Any suggestions appreciated.