well no SHSH, because i don't have it...but I see I can get it for 4.1 and there is my next question, can i downgrade to 3.1.2 or 3.1.3? I have seen a tutorial for broken power button, how to downgrade, and jb, this is the link and I would like, please, to tell me if this is ok, even if I have 4.2.1. the only reason i want to downgrade is because I don't know if there is any method to jb it...with the power button down, oar maybe something like in this video, but for 4.2.1 ... I really don't know what to do

YouTube - Jailbreak/Unlock iPhone 2G 3.1.3 with Broken Home/Power Button

Wow, i remember something...i have tiny umbrella and it appears some shsh saved... it says: all saved shsh and below that it says 4.0, 4.1 and 4.2.1. ... from now on how can i downgrade to 4.0 with broken power button ? any help please ^^

As long as you were legally on 3.1.x before you went to 4.0 then you can downgrade again. You should have the IPSW on your hard disk already. We cannot provide download links for iOS 3.1.3 or 3.1.2 or 3.1.1 for the iPod touch 2G

iOS versions before iOS 4.0 are not free for the iPod touch.

Step by step on how to downgrade.
If you are trying to downgrade to an iOS 4.x version, first open TinyUmbrella and click "Start TSS Server"
Find correct IPSW (we can only help you with download links to 4.x IPSW for iPod touch)
Connect iPod to iTunes
Shift-click on Restore button in iTunes (option click if you are on a mac)
Browse to the IPSW you want to downgrade to.
Click OK - it should proceed without error.
If any errors occur, first try Tiny Umbrella's exit recovery mode.
Otherwise we can't help you without a restore log http://www.hackint0sh.org/f137/130802.htm

I already downloaded the IPSW for 4.0 and I will follow these steps well, wish me luck and I will stay here in case of anything thank you very much

It was a very smooth operation thank you very much, I'm so happy thanks a lot yay