K800i phone just turn into white screen

Screen is ng. See if your provider will replace the phone at no charge.

charge your battery with external charger or check your phone with full charged battery.....

From Apple Support:
Display shows a white screen

1. Turn iPhone off and turn it on again.
2. If the iPhone will not turn off, try to reset it. Press and hold the Sleep/Wake button and the Home button at the same time for at least ten seconds, until either the Apple log or battery symbol appears. If the battery symbol appears, continue to charge iPhone until it is fully charged.
3. If that doesn't work, try restoring the device.

Possible to rectify with Wotan Server to repair the EROM which is checked before firmware is flashed. You will have to buy credits and a data cable. Follow instructions pressing key 2 and 5 together. You may as well update the firmware after this process. Google around you will find this is an issue

let it sit in the charger for 1hour then try to turn on your phone. it could be that the charger cannot charge the battery and turn on the phone at the same time and the battery is too weak to turn it on and needs a better charge.

White Screen Of Death. Quite common on Sony Ericsson phones. My K800i does it every time its battery shuts off while it's on (so I try to make sure it doesn't). You need to (google terms) reflash sony ericsson phone Maybe also first backup GDFS The photos, except those on the memory card, and other stuff will be lost, I'm afraid. But good news is that your contact list can likely be saved by backing up the GDFS.

I had a similar issue, whereby my phone would turn on for 30 secs then the screen would go white and the phone would switch it self off then on.

After a lot of messing around even throwing the phone around the place. I took out the memory card and the phone worked fine. When I put the card back in, the phone started misbehaving again, so I guess the card is knackered.

Take your SIM card out.
Make sure your phone battery is fully charged.
Press * 3 send at the same time and turn the phone on. Keep them pressed until the reset screen appears.
Give it time to reset.
Your phone might also benefit from a software update.

If you can try another fully charged battery, in your phone and it works then it might be a dodgy battery problem. leave the phone off to charge the battery for 10 hours and see if its better.

So you mean to say your phone won't turn on at all? Have you tried removing the memory card, sim card and then the battery, put the sim card in and battery, turn it on without the memory card and see if it works...