Up, Down Power is how to turn the phone on after a soft reboot (soft reboot is press the power button then slide to power off). After you hold and release the Power button to power back up you get the white screen. When the white screen is finished, you get the keypad. Or Perhaps you got a corrupted download.Thanks Bear7962.
‘Up, down, power…’ is the soft reset. The problem, I found, was with the login dialogue box immediately after a soft reset not bringing up the keyboard. There was never a problem with 15.6.1 and earlier. Although I installed 15.7, I then spotted the 16 upgrade and installed that, so I don’t know if the bug came in with 15.7. (It may well have done at the end of installing 15.7, but if it did, I did not take any notice at the time.)