If you replaced  Kindle Keyboard  Screen ED060SC7(LF)C1 with not original (all new screens aren't original) then there is no Waveform data written on screens EEPROM  chip.
  If you changed screen with battery attached to motherboard  then waveform is already loaded to motherboard from original screen and replacement screen will work correctly until battery will be completely discharged or Kindle will restart unexpectedly.

  To fix this you need to boot your Kindle with old screen attached.

  If you binned it then you can buy this cable.

  Step by step instructions:

 Switch Kindle off, open back cover, disconnect your screen cable (try not to bend back more than 90 degrees as it is possible to damage it on the plastic edge of Kindle), connect this cable and reboot Kindle by keeping On button for 30 seconds then releasing it. Kindle will reboot and load waveform from this chip. Leave Kindle alone for 5 minutes ( to be sure that it rebooted completely as you will be doing this blind without screen). Then move power button and release it to switch kindle off. Then disconnect this cable and reconnect your screen cable. Switch Kindle on and when it starts  switch it off again. Screensaver should be displaying correctly now.