I think I screwed my iPhone, but am asking for help anyway!
EDIT3: PROBLEM SOLVED, I'm editing this so that people don't read this long text for no reason unless they want to.
Hey there :) I'll try to describe everything with as much information as I can. Sorry for any bad english, it isn't my main language.
I had in my hands an iPhone 3G with FW 4.2.1 and BB 05.15.04 and I had to jailbreak and unlock it.
I downloaded the 4.2.1restore ipsw and Redsn0w 0.9.6b6. I ran Redsn0w. I selected Cydia + BB change during the instalation. Everything worked fine. iPhone was jailbroke and had the iPad's 06.15.04 BB on it. Through Cydia I unlocked it. It was all working well.
But it wasn't good enough. I noticed the system was kinda laggy. So I googled it and read many people saying the reason was the 4.2.1 version and that it was possible to downgrade to 3.1.3 and the iPhone would run smoothly again.
I downloaded the 3.1.3 restore ipsw and shift clicked the restore button on iTunes to select it. I had the 1015 error on the mid end of the process, but that was expected according to my reading. After that, I couldn't jailbreak the iPhone again, so I tried to go back to 4.2.1. Received the 1015 error again, but I thought it was expected. But by now the iPhone was stuck in recovery mode. All I see on my iPhone's screen is the iTunes logo with the iPhone cable trying to connect on it.
RecBoot and TinyUmbrella will get me out of Recovery screen, but it takes me right to the centered apple screen and after ~10-15 seconds I get back into recovery mode. It's an infinite loop recovery mode.
I suspect the problem is that I tried to jump from version to version while having the 06.15.xx BB and now I'm stuck, but I'm a total noob and have been only reading about these things for the last 3-4 hours, I didn't have any previous knowledge (aka stupid douche doing what he wasn't supposed to do).
Any restore I try to do returns me a 1015 error. If I try to JB anyway with the latest ipsw and redsn0w it stucks on "Installing Activation Bundles". If I try older versions (3.1.3 that I used), it stucks in the pineapple screen and after 10minutes resets. All of those gets me back to recovery screen.
TinyUmbrella says my fw is currently 3.1.3. I don't know if that is a missread, if it's stuck on it's last successfull read or if it is the truth.
Here's a pastebin of my recovery log:
2010-12-11 03:18:22.077 [3456:175c]: restore libra
I'm currently on Windows 7 64bits, iPhone 3G and iTunes 10.1.0.56
I thank in advance any soul that has some insight on this case! Please let me know if you need more information.
EDIT: I'm doing my restore attempts both with simple restore and DFU mode and on 2 different computers.