Iphone 3G shows only itunes symbol and usb connection?

Yesterday i was trying to update my iphone 3G from 3.1.1 to 4.2.1 but after completing "Restoring Firmware" process it turns off automatically and then it only shows a usb cable connection showing to the itunes. I tried to search lot of things on internet but it can't resolve my problem. I already tried Redsn0w, tiny umbrella, custom ipsw but it still shows that error. If anyone here faced this problem than please please please reply me with a proper solution.

Youll need to get out of recovery mode or dfu mode

or

if you didn't have the SHSH Blobs before you installed your IOS then youll need to ONLY USE THE IOS for the SHSH BLOBS you have ONLY
use TinyUmbrella to check your BLOBS 1st
this might be your issue,
so to be clear

you can only use the IOS to which SHSH BLOBS you have
example
6.1.3 SHSH BLOBS can use 6.1.3 IOS

in your example: you have 3.1.1 which means you can use 3.1.1 SHSH BLOBS for your 3.1.1 IOS

if urs says only 3.1.1 BLOBS then you can only use that IOS unless you update to the newest IOS
which is 6.1.3 cause APPLE isn't signing SHSH's anymore

i'm on a iphone3gs updated from 3.1.1 to 4.1.2 with the proper blobs
thus i can only use 4.1.2 IOS & jailbreak