What is happening to my phone

[AC Question]

All of a sudden my phone went black like it was shut off and then when I tried to turn it on there was a blue screen and it said download in the middle with a bar and underneath it says do not turn off. On the upper left corner it said factory mode with other stuff such as Knox warranty void etc. It was like that for a while and then it went black again and now when I try and turn it on it shows the battery sign and it occasionally flashes this triangle in the battery sign with something that looks like a thermometer

 

[Tim1954]

Ignore the do not turn off and long press the power button until it either boots, or turns off. Press and hold the volume up and home buttons, while pressing power button until you see the logo. Release the power button but hold the other two until you get the menu with wipe ootions etc. If you get the robot falling over, just wait for the menu to pop up. Scroll down to wipe cache partition (using volume) being very careful not to select factory reset!! Follow prompts carefully and your device should reboot much refreshed and bug free hopefully.
Not knowing what device you have, this is a Samsung trick, if you have other device maybe google wipe cache partition for that device to be sure.... Good luck