Support Help! Warning!! A custom OS can cause critical problems MY phone (Samsung S3) just went off today and started flashing the Samsung logo. I have taken out the battery multiple times and tried to restart the phone. Only once did it restart but then after ten minutes went back to the logo.
I tried to press HOME VOLUME UP and PWOER and nothing happened. Then i tried HOME VOLUME DOWN and POWER and i got the screen for Support Help! Warning!! A custom OS can cause critical problems....after a while it goes back to the logo flashing.
I cant restart or reboot my phone. 

Please help.
I had the same problem with my S4. Whenever the phone goes off and I try to turn it back on the annoying 'Warning' Custom os comes on and I couldn't turn my phone on.

I read a few articles and discovered that it has to do with your volume button. I dropped my phone a few days ago and read that if the volume button is stuck that this happens. So I went to the kitchen and go a sharp knife, put the blade to the side of the volume button and pulled it up on both ends, to my amazement, the phone turned on!!! (make sure its plugged in because whilst that warning is on the phone doesn't charge)

Now I have to go and get my volume button looked at because it is a stuck volume key that causes this. It must be a secret sequence that the phone companies use to change an os. I also read that Knox program can cause it, nevertheless, the volume button release worked.

Hope that helps.