Sony VGN-AR520E - Green lines on BIOS , cannot load windows

Hi guys ,
Hope that you'll be able to assist ...
I have a 4 years old Vaio VGN-AR520E . It has a NVidia 8400MGT GPU .
Till two months ago it worked properly . Suddenly it started to show from time to time green vertical lines and horizontal lines of white dots on restart , at the BIOS stage .
When these lines appeared , I had to go to Safe Mode , to disable to GPU in order to make Windows 7 loading . At the times the green lines were not present , the Windows 7 was loaded properly , having the GPU working properly .
In the last two weeks , the green lines and the white dots are appearing every restart and because of that I am able to get into Windows 7 only after I'm disabling the GPU ( I think that it is called Stamina mode for other models ) . It makes my laptop almost worthless...

I am not sure if it is related to this problem but when it appeared I noticed that the right up corner area of the laptop , where the power button is located , is very hot . Using HWMonitor I was surprised to see that the GPU temperatures were around 85-100 Celsius degrees very often , having only 10 tabs of firefox opened . I cleaned the fan and the temperatures are much lower now, between 50 to 70 degrees , but the problem remained the same - green lines at BIOS and can't load the Windows by having the GPU enabled .

I know about the 8400 GT problem that is common on many models but my model VGN-AR520E is not recognized by Sony to have this problem ( but other close models - VGN-AR3XX series - are in Sony's list with this problem) .
I really need you help with your thoughts if it is possible to fix this problem and if so , how . I would like to try to replace the BIOS battery ( btw - please mention where this battery is located if possible ) for a few minutes hoping that it will help . I thought maybe to reinstall the OS but to me it looks like a hardware problem and not a software one , so I don't know if the OS reinstallation will help in this case ...

What's your opinion ? What should I do ?
Thanks in advance .

 

nVidia graphics chipset need to resolder.
Unfortunately, your laptop is not covered by Sony recall for nVidia chipset.
PM me if you want to fix it.

 

Thanks for the reply ngvuanh .
Yeah , I know that it is not covered by Sony's recall and I really wonder why because according to the nvidia chipset details it has exactly the same chipset version and production as the ones that are included in Sony's recall .
I contacted also Sony's International support and they told me the same - that my model is not covered ( no matter that it has the same problem , with the same behaviour and the same chipset details as the ones covered in the recall ) and the only thing that would help is to contact the local Soy Center and to try to get it fixed there .