Error 8002F147 while trying to update firmware3.50

Hello,
I have been aiming to solve my ps3. I have tried to update firmware 3.50, but I am getting 'error 8002F147', when the install process in 20%.
I have also formatted the disk many times, and tried installing a previous version of this software. Recently, I also tried to update 3.56
If anybody knows how to repair this problem, please help me.
It has been more than 1 months without my ps3! Please help.
Thanks.
