My iphone is stuck in recovery mode, how can i fix it?

I have iphone 3g and i tried to install a new firmware but it failed and now my phone is stuck in the recovery mode (i tried to exit by holding the home and power keys but comes back into the recovery mode again). I totally backed up my phone before i do anything but the problem is that i can't restore because when i click on restore, it wants an IPSW file (which i'm currently downloading version 4.2.1) but i'm afraid if i install that, i will lose all of my files like messages, contacts, notes, etc, or won't i?

This happened to me before I used this:

Step 1.
Download TinyUmbrella for your PC. It works on Any computer

Step 2.
Connect your iPhone in Recovery mode to your PC if it isn't connected already.

Step 3.
Open TinyUmbrella.

Step 4.
Let TinyUmbrella recognize your iPhone in Recovery mode.

Step 5.
Once it recognizes your iPhone, you can kick your iPhone out of the Recovery mode by tapping the button "Exit Recovery".
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But if you don't want to do it that way:

Firstly, you wanna bring your ITunes up. Secondly you wanna connect your ipod to your computer. (You should know how to do this) Next, on your computer screen a sign should pop up saying that "your phone is in recovery mode, you must restore you phone before using iTunes" What you do now is click ok And then near the bottom of the Itunes you just click Restore or Find the Restore button on iTunes, It will be there somewhere. Once this is done it will be working

Hope i helped! Xx

Okay the other guy read it wrong, what happened to you was that the restore didn't finish right? If it did get almost right to the end then say i hate you, then use his method, if it failed from the start or midway just restore from a backup in itunes after you upgrade: D