iphone 6 wont work. just showing apple logo and white background

Okay, you would need to contact Apple Support. Follow the steps below:

If you need more help

Contact Apple Support to set up service if you have any of these issues:

• You still see a black screen after charging, force restarting, or following the steps in this article.
• You see a black screen, but you can hear alerts, sounds, and vibrations.
• Your screen is on, but it doesn't respond when you tap, slide, or try other gestures.
• You can't force your device to restart because your Home button or Sleep/Wake button is broken or stuck.
• Your device is stuck on the Apple logo, displays a solid color, or isn't recognized in iTunes.

Hello,

Double check with the following steps:

If your device turns on but gets stuck during start up

If you see the Apple logo or a red or blue screen during startup, try these steps:

1. Connect your device to a computer and open iTunes. If you don't have a computer, try to borrow one, or go to an Apple Store or Apple Authorized Service Provider for help.
2. While your device is connected, force it to restart.
   • On an iPhone 7 or iPhone 7 Plus: Press and hold the Sleep/Wake and Volume Down buttons at the same time.
   • On an iPhone 6s and earlier, iPad, or iPod touch: Press and hold the Sleep/Wake and Home buttons at the same time.
3. Don't release the buttons when you see the Apple logo. Keep holding until you see the recovery mode screen.
   
4. When you get the option to restore or update, choose Update. iTunes will try to reinstall iOS without erasing your data.
   

iTunes will download the software for your device. If it takes more than 15 minutes, your device will exit recovery mode and you'll need to repeat steps 2 and 3.

More info here:

If your iPhone, iPad, or iPod touch won't turn on - Apple Support

It seems that sth is wrong with the operating system that prevents the phone from booting up normally. In the case that recovery mode doesn't work for you, you might need Device Firmware Update (DFU) mode. As opposed to recovery mode, DFU mode stops your iPhone from activating the boot loader or iOS so that you can connect it to iTunes and restore iPhone and start fresh.

Similar operation steps with recovery mode, but DFU mode requires a more precise set of actions. First, plug in your iPhone to PC and open iTunes. Then turn off your iPhone, hold down the power and home button together till you see the Apple logo. Next, release the power button while continuing to hold the home button. Finally, wait for the iTunes to tell you that it’s in the restore mode. In this way, you can restore your iPhone to factory settings or load your latest backup file, as described in the Fix iPhone stuck on Apple logo article.

But if this method is still useless for you, the best choice for you is get help from Apple Support.