WSoD of iPhone 3GS

The power button of my iPhone 3GS was not working and was managing with Assistive Touch. When I charged the phone after a long gap, may be an year or two, I found to my dismay, the screen was stuck in 'connect to iTunes'. I was not able to restore or reset it. At the end of every restore process in iTunes, I get a message that "There is a problem with my iPhone" and the phone was back to 'connect to iTunes'.Pl. note I could see the process going on at different stages in iPhone during the restore. Finally I decided to replace the defective power button on my own and somehow replaced it with great efforts. Mind you, here, NO spare parts,repair services and Apple support are readily available for iPhone 3GS.After the assembly with new power button, what do I get! White Screen of Death! That too without Apple logo! Hard reset with now working power button and home button did not help.After releasing the buttons screen turns black. So I dismantled the phone again and checked all the ribbon connectors are seated properly, as advised by various sources but the WSoD will not go. I put the phone in recovery of mode with the help of a third party software repair tool( only free trial version as I was not sure about the paid version) With the phone in recovery mode, I tried to restore the phone with iTunes. I could see the restore process progressing in the computer, even though iphone screen was in black, sometimes white, during the entire process. When the restore is completed with the phone still connected to the computer, while the iPhone is accessing the iPhone, bang! The same message pops up "Your phone has got a problem. Get it repaired by Apple services". Which is simply not there for iPhone 3GS! I am really stuck now like my iPhone!

Can anyone help?