Hi there happy to help.
Please try the following.
Unplug the Kindle from all outside sources.
Hold the power slide to the right for 20 seconds.
The Kindle should flash and restart. Problem free.
Let me know,
OK, how old is the unit?
OK, complete no brainer.
Amazon is one of the best companies we deal with as far as warranty replacement goes.
Contact them here, tell them what we have tried and they will send you a new one, no problem.......
And here's a little extra for you.......
If you find yourself out of warranty on the Kindle(past one year), and something like this happens.......call them anyway. I've had alot of customers that Amazon still replaced their Kindle for them. They are very good with Kindle customers.