macbook pro will not boot up

MB Pro will not boot up. This morning I checked emails and then checked for OS update, was told there was one, so I selected that (but not upgrade to Sonoma or Safari). Got notice that it would take 20 minutes, so I left it. A couple hours later came back and the screen was black. Tried to power on with no success. Tried holding power button for a good 10 seconds, tried while holding the shift key; at least 10 times in total. Once or twice got the Apple logo and maybe short message, but only for a second or two, and then back to black screen.

Spoke with Apple support guy, no help. I have Genius Bar appointment at nearest store for 4:30 tomorrow, but I would like to see if any of you have any suggestions to get me up and running sooner.

MacBook Pro M1, February 2022, OS is Ventura probably current less one update.