1. Maybe my memory is incorrect, but I thought that series doesn't have a standby mode and briefly sliding the power to the left shuts it down completely when on battery. However i think while charging if you slide the power to the left it shows the message 'Charging battery, slide the power key to turn on' or similar appears then it is in standby, or maybe it's just screensaver mode. If on charge and you hold it to the left until that message disappears then immediately disconnect the power source and release the slide it will go off completely. If you leave it connected it'll reboot however. That's all from memory mind you and mine's a bit shot.

2. Hold lower right corner while off then power on, follow the prompts.

About your 'BTW': Are you referring to the car ciggy charger or a 'generic' 5V power source, because if it's doing that with the car charger either it isn't a Garmin branded charger or the ~17-18 Ohm bridging between Pins 4 & 5 resistor has failed. See here:
Code:
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About your PS: That's quite likely because you can do a lot of damage flashing in preboot if you don't know what you're doing.