I'm unable to restore my Iphone, need some

I have Iphone 3G i don't know which firmware i was using on this, but now its on recovery mood. I have downloaded almost all the firmware versions and tried one by one on my phone, but failed. I get errors like 1015, 2005.
and now its not even showing any display when i keep on pressing the power button, please help me what to do now

Plug the phone up to your computer then hold the home and power buttons for 10 seconds (be sure not to count too quickly) then after that 10 seconds release the power button and just hold the home button

That error notification means there's a problem with your hardware. A simple hard reset like suggested above will not solve the issue. You are going to have to go through Apple or someone that repairs iPhones.