It's been reported in other threads that if you drain it that far, you might need to charge it once with a USB-C charging cable to revive it. I'm not sure why.
Then, as @tophneal brought up, it might be executing a software loop or the SOC has otherwise crashed and is "running" with no signs of life. If that's happening, you need to hold the power button for twenty seconds or so to get it to turn off. Then press it for a second to get it to turn back on.
But have no fear, it's impossible to "brick" the PBP; and nearly impossible to get to a point where it just won't boot.
Don't worry about the reset button; you shouldn't need that unless you've written something to SPI F-ROM.
Then, as @tophneal brought up, it might be executing a software loop or the SOC has otherwise crashed and is "running" with no signs of life. If that's happening, you need to hold the power button for twenty seconds or so to get it to turn off. Then press it for a second to get it to turn back on.
But have no fear, it's impossible to "brick" the PBP; and nearly impossible to get to a point where it just won't boot.
Don't worry about the reset button; you shouldn't need that unless you've written something to SPI F-ROM.