Sony xperia S Screen freez in color and turns white

[RipperBK]

Hello all!

I have a Sony Xperia S and i had no problems with it unitl now. It startet about 5 days ago, i was doing something outside and come in to see what's up on Facebook and in about 10min of use the screen starts to get that retro style color. Something like this first https://communities.intel.com/servlet/JiveServlet/showImage/2-153170-227597/IMG_20120402_223344.jpg and then this http://i1.ytimg.com/vi/ofuNEkncGQk/hqdefault.jpg (this are random pics form google and sorry if another company logo is on it). When i push the volume up and down buttons the phone reacts, and when i turn off the screen and get a message from Facebook i get the LED notification. But when i try to turn on the screen i get a black screen with no response. After some time the phone is good again and works fine, then again and again. 

I tryed all options: hard reset (sometimes it works), repair software, delete all apps leave only those that are from the factory. 

I do a lot of programming and know IT architecture well (i only programmed on the phone over AIDE that is from Google play store), it looked to me like a graphic issue (and still is i think) but then i downloaded the Xperia Diagnostic and done all the tests and the phone is OK. 

So the hardware is ok but the software not from my position of view. I don't trust the services here in my land it's like to give the phone in hands of a child and i know that i have more qualifications to repair it that them (Sony should really do something to make that better in my country). 

Anyway I tryed to make the problem clear enough. Can someone help me with my problem? 

[RipperBK]

I see the problem was never here and nobody has a good idea. 

I was experimenting and i have a new fact: when the screen was going colorful i lightly pressed the back of the phone and the phone has come back again in the normal state. Then i was doing some tests to see what te really promblem is...

Everytime the phone was in horizontal state it turned off ( with a little wing force or some time in this position).

I got now a little paper inside the back case to do some pressure on it and the phone works fine.

Now is the problem how to fix this forever? I know that on this position is the battery and there is probably something with it...

Can anyone say me something good? 

PS: The phone is like new, never fall down or something like that.