Car won't turn off

Try pressing the POWER button down for more than three seconds. Hopefully that will force the car to IG-OFF.

 

Is the Prius READY?

If no, then open the hatch, find the 12V battery in the right-rear corner, and disconnect the battery by removing the negative cable where it bolts to the body. Then the car should shut down.

If yes, then you should be able to drive the car.

 

The battery is in the hatch area, not the hood. You need to remove the triangle shaped hatch floor piece as well as the trim piece adjacent to that, to see the 12V battery. You would need a 10 mm socket or open end wrench to remove the bolt.

Alternatively, if you lack tools, you can examine the positive battery cable and may be able to see a connector that you can remove by hand.

 

This is because the body ECU thinks the car's speed is some value other than zero since the combination meter is not working.

If you wish to be persistent, open a rear door, lower a rear seat back and crawl into the hatch area, bringing a flashlight along. Remove the folding hatch floor and look at the rear of the black plastic tray covering the spare tire. Notice a small rectangular door near where the hatch lock is.

Open the door and find a shiny metal lever which is the mechanical hatch lock release. Move that lever and apply upwards force on the hatch, to open it.

 

100% chance that the battery will be dead tomorrow if left as-is.

Given the above, your car is in IG-ON mode which places a very heavy drain on the 12V battery. Your first post was more than one hour ago and by now the battery has been drained ~15 Ah. The battery capacity when new is only ~40 Ah.

Depending upon how old the battery is and its state of charge prior to this incident, the actual battery capacity may be much less than 40 Ah.

Once you are able to disconnect the 12V battery, you should put the battery on a charger to improve the likelihood that the car might become READY tomorrow. If you can select the charging rate, use a 4A rate.

 

1. If you have a battery charger, you should hook it up now and let it charge the battery until tomorrow morning. If you can't get to the battery, you can hook up the charger to the dedicated positive jumpstart terminal in the main relay/fuse box next to the inverter.

Press HARD on the latch at the front of the relay/fuse box lid, then pivot the lid up and remove it.
Find the red cover over the jumpstart terminal and release the latch, then pivot the cover.
Attach the positive charger cable to the exposed terminal.
Attach the negative charger cable to unpainted body metal, for example one of the strut nuts behind the relay/fuse box.
Turn on the charger, use a 4A charging rate if possible.

2. If you cannot get the car started tomorrow, then try to get the gear selector into N to help getting your car set up for towing. This will be facilitated if you have restored the 12V battery to full-charge.

If you can't get the gear selector out of P, then the tow truck driver will have to drag your car using the winch. This is not the end of the world but is not an elegant way to proceed.