Hello & Welcome to Just Answer,
Sorry I didn't see your question earlier and to hear of any issue you are having with your device.
If you still need help you with this device, let me offer the following:
1) FIRST, I have a link to the electronic (PDF) version of the FULL system manual for this device below. That should get you better acquainted with all the features and functions of the device.
Click here --> http://static.garmin.com/pumac/Drive_40-50-60_OM_EN.pdf
Here is the same information, EXCEPT in a "web-based" form >> CLICK HERE <<
2) NEXT - it sounds like you have the device connected to a computer (because of the display showing an image of the device connected to a cord - and perhaps a "computer"). It is NORMAL for the power key to do nothing when the device is connected to a computer.
So to power the device OFF, first "Safely Remove" the device from the computer (EJECT it), and then physically remove it from the USB cable. If needed, press and HOLD the power key and if needed touch the "yes" to power down the device.
NOTE: Powering ON the device is just the same process of pressing the power key - until the screen comes ON - then release the power key.
These devices will USUALLY power ON - when connected to power in the vehicle - using the vehicle power adapter that came with them. And be aware that SOME vehicles MUST have the ignition turned ON to supply power to the vehicle power adapter.
That should be enough to get you STARTED with using this device. Please take the time to review the manual links I sent, and let me know if you have any more questions.
If this has helped answer your question(s), please take a moment to rate MY service level (5-star is my goal) so that I get credit for my time helping you with this question.
You should see some "stars" (and SUBMIT button) to do that, but please let me know if you do NOT see them (you may have to REFRESH your screen) or can not use them.
Take Care & Travel Safe, Greg A.