Why has the light in my kindle fire gone off i cant read anything

Do one thing to get rid of this problem, Just visit kindle fire tech support website for instant solution of your problems. No matter what issues you encounter, just call or visit our website.
Amazon Kindle Fire Tech Support Number

I would dump the files of any books you have read and no longer need, you may have a problem with the memory not having any free space.

Files in the operating system get corrupted You need to reinstall the operating system you can get the help from amazon support
Kindle Technical Support Registration 877 690 9305

Yes, Kindle is a name used for all the Amazon tablets and e-readers.

Kindle 2, 4, 5, 7, 8
Kindle DX
Kindle Touch
Kindle paperwhite (1,2,3 generation)
Kindle Voyage
Kindle Oasis
Kindle FIre 7
Kindle Fire HD 6, 7, 8, 8.9, 10
Kindle Fire HDX 7, 8.9

And I probably missed some in here.

Check the Serial Number You can find this sixteen digit code in the box your Kindle came in or when you click on Settings and go to Device Info. Find your specific generation or type based on the first four characters. Kindle 2: B002, B003 Kindle DX: B004, B005, B009 Kindle 4: B00E, B023, 9023 Kindle 5: B012 Kindle Keyboard: B006, B008, B00A Kindle Paperwhite (2012): B024, B01B, B01C, B01D, B01F Kindle Paperwhite (2013): B0D4 or 90D4 Kindle Touch: B00F, B010, B011 Kindle Fire (2011): D01E Kindle Fire (2012): D026 Kindle Fire HD 7(2012): D025 and D059 Kindle Fire HD 7(2013): 00D3 and 00D2 Kindle Fire HD 8.9: B0C9, B0CA, B0CB, and B0CC Kindle Fire HDX 7: D0FB, 00FB, 00FC, 0072, 00FD, 00FE, 0073, 006C, 006D, 006E Kindle Fire HDX 8.9: 0018, 0057, 005E, 00F3, 0019, 0058, 007D, 007E, 007F - See more at: http://glyde.com/glydecast/how-to/which-kindle-do-you-have/#sthash.bAbYPdzQ.dpuf

Reset Kindle Fire When it Won't Turn on or Charge

www.lovemyfire.com > Kindle Fire Problems

However, sometimes when it locks up you can't tell because the screen goes dark, either ... it's already on but is locked up and thus won't charge or work properly. ... 15 minutes to make sure it gets enough charge, and then try turning it on again. ... If this tip (or anything else on my site) helps solve your Kindle Fire problem ...

Amazon.com: Customer Discussions: My Kindle won't charge

www.amazon.com/forum/kindle?_encoding...

Amazon.com, Inc.Jan 3, 2013 - If you can't see a Contact Us button on this page, then go to .... What canI do? I sent an e-mail to Amazon but have not heard anything. My Kindle is frozen and won't ...
Mar 31, 2014
How to unlock a Kindle. Lock won ...
Jan 27, 2014
Kindle paperwhite won't turn on
Nov 6, 2013
My kindle won't turn on....green ...
Dec 12, 2011
More results from www.amazon.com

To buy and deliver Kindle content, register your Kindle Fire to an Amazon account. Registering also allows you to transfer purchases between devices and Kindle reading apps. To register your Kindle Fire: From Home, swipe down from the top of the screen, and then tap More. http://www.amazon.com/gp/help/customer/display.html?nodeId=201729910

Give enter to password, in blank, withoul inputting anything. Maybe it accepts it as password.
The other possiblity is that you've been pranked and someone defined a password

Here you have a tutorial for Password Remove:

Kindle Fire Password Remove

If you can't get the password, you should do a Factory Reset.

Here you have some video tutorials how to do

Kindle Fire HD How to Reset Back to Factory Settings

Kindle Fire HD how to reset when locked up EpicReviewsTech CC

How to Factory Reset Amazon Kindle Fire Tablet Tutorial

Read these Troubleshooting Your Kindle Fire HD 7

See here: Amazon Kindle DX Support

Once you have the machine running to read anything, the Kindle user manual is a pre-installed eBook on the device and also available for free via the Kindle storefront in case the previous owner deleted it.