XPS 15 9560 power settings behaving badly...

I had a storm blow through earlier today, that caused the lights so dim & flicker on & off a few times.

When I went to use my laptop, n XPS 15 9560, that is connected to a Dell P2717H via HDMI cable, it was off, assuming as a result of the power & turned it back on, Once splash screen & eventual log in screen came up, I closed the lid & monitor went black, then to the scan mode (although I have it set to HDMI) & a message popped up on monitor saying 'No HDMI signal detected from your device'. I opened the laptop lid & display came back on monitor, but will not stay on when I close the lid!!! I ran diagnostics from the Dell Support Assist & it found nothing wrong. I checked for updates & installed any that were needing to be updated & no change. I reset power settings back to default, restarted, changed them back & still no change! I even changed the HDMI cable & still no change... I do have the option set to do nothing when closing the lid & laptop plugged in, but computer just isn't doing as I have he settings set. I usually leave the laptop on most of the day, with power settings to never turn off display or let the computer sleep, but now cannot get back there! I can leave it on, even with lid open, but after a while (I haven't sat here & timed it yet) I can come nack & it will be off.

Any other suggestions?

Thanks!