4.3.1 White screen problem when phone exits sleep mode iPhone 3G

Hi all,
Firstly, Im French so please forgive my English...
I have a big problem since I installed the latest 4.3.1 version of iOs on my Iphone 3GS. The installation process ended with no problem, I get all my apps, SMS, contacts unchanged etc... Perfect at first time.
But as I left my phone a few minuts, he entered in sleep mode (Im not sure you call it this way? When the phone is unused, the screen becomes darker and then is off) as usual.
When I pressed the power button to get the Slide to unlock screen, nothing !! Instead I get a completely white screen.
The screen stays white, but everything is active under it!! I can slide to unlock, launch apps (I can hear them)... but I cant see anything. I can stay pressing for 3sec the power button, and slide to shut down the phone, no problem.
The only way to get the screen working is to reboot the phone.
I have the same problem when calling : I put the phone close to my ear and the screen gets dark. When the call is finished, I take the phone off my ear and the screen is now white and I cant see anything. Again I have to reboot to get a normal display.
So the only solution I have now is to cut of the automatic sleep mode, and use the freehand kit when calling.
Anybody heard of this problem? I have my phone since a year and a half, never had any problem. This problem just appeared when I installed iOs 4.3.1.
Thanks for the help !
Message was edited by: Jemetouche
Message was edited by: Jemetouche
iPhone 3GS 32gb iOS 4 iOs 4.3.1