why my phone enters download mode on its own?

[psychocryo]

Hi,

I'm new here and in need of help if anyone would be kind.
i posted my problems in my phone's forum which is Asus Padfone. However i decided to post here as well to get a broader help since it might be an issue with android os in general.

Yesterday i did an update to jelly bean which was recently available for my phone.
all went smooth and ok for the whole day.

when i went to bed,i plugged in my charger and when i woke up in the morning the screen is showing it's in download mode:

http://img.schattorie.nl/images/77193696198737425427.jpg

I dont know how it got there and since i dont want to damage anything, there was an option to reboot phone if im not mistaken.it was the first in the list. so i selected that and my phone reboot.
After that i notice my ringtones are different and i found out it's gone.

and to top it off..many of my files in the sdcard is gone..even my hidden files and other documents and image files..not all of it is gone but quite a lot.
why did this happened?? anyone have a clue?

 

[patruns]

When you do a factory reset you lose most of your data. As to how you ended up with a screen showing you are in download mode, I can't answer that. I have never see that screen.

 

[meyerweb#CB]

What phone do you have, and what version of the OS did you update to?