Hard reset

• Hold on/off button for 15 seconds. The device turns off.
  
• Hold on/off for one second to turn on the device.
  

• Hold on/off button.
  
• Select on/off icon -> Yes to turn off the device.
  
• While holding Lap/Back button, hold on/off button to turn on the device.
  
• Select Yes.
  

• Power off watch (press and hold Light, Yes on prompt)
  
• Press and hold Start/Stop and Lap/Reset.
  
• Press and hold Light (three buttons should now be pressed in)
  
• After first beep, release Start/Stop.
  
• After second beep, release Lap/Reset.
  
• Release Light.
  

I've killed my F935 by either loading a course that contained some errors or by too long activity or both. During the activity I observed unusually slow responses to the buttons I've pressed. It run out of battery before the finish line. Later, after charging, I could not power it on. It displayed only a blue triangle and did not go further. Method 3 has solved it. Thanks!!!

Very frustrating advice.

There is no "Lap/Reset" button on the Garmin 935.
There is no "On/Off" button on the Garmin 935.

The button labels on the watch are (counter clockwise):

Light
Up
Down
Start/Stop
Back

To do a hard reset, first press and hold the 'Back' button, then press and hold the 'Light' button.

You should then be prompted to clear user data. Let go of both buttons and select 'Yes'.

Watch will do a hard reset. Respond the the prompts.

Light = On/Off

Back = Lap/Reset

As manual indicates.

Thank you, method 3 was succesful!

It worked for me!  I deleted course using windows file manager, which locked up the watch until I did this. Now it will only accept one course, so factory reset is next. *Don't* delete courses using Windows file manager!