IPhone 3GS 3.1.2 ( I NEED HELP PLEASE READ )

[zig9449]

Yes, it turns on .. Is there a software to get in dfu mode without power button

No. Sorry mate. Cannot be done.

The only way to enter DFU is with both home and power buttons.

Power buttons are cheap, and easy to replace.

 

[Thomasjtsi]

If the power button is not working then this is the part you need to replace... iPhone 3G/3GS Headphone Jack Assembly - iFixit. While you can buy the actual button itself here... iPhone 3G and 3GS Power Button - iFixit. This is only the button itself and not the internals underneath that aren't working. Here is the How-To on replacing the first part I have listed... Installing iPhone 3GS Headphone Jack - iFixit.