Hello and sorry you're having problems. A crack in the touch LCD display of the Kindle is a hardware fault and requires replacement of the outer screen and digitizer to fix it. The digitizer is the inner layer of the screen that responds to your touch commands. In order to fix it you would need to purchase and replace this part, which requires a bit of work and a steady hand, but can be purchased at the link below for around $50 (1st generation Paperwhite):
What you can try first, even though it's not likely to be a fix, is to perform that reboot (power button for 40 seconds) up to 4 more times- making sure you wait a full 60 seconds for it to reboot. If that does not work the digitizer does need to be replaced.
If this is not something that you're comfortable with then a 3rd party Kindle repair service (like Mission Repair) will charge close to $120 for this type of fix at the link below:
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