HELP PLEASE! jailbroken iphone 3g will not restore in itunes

[rbchanlidd]

I am a complete idiot when it comes to jaibroken devices and things of that nature, so PLEASE bare with me.
I have a jailbroken iphone 3g with what i believe WAS 4.2.1, i turned my phone off and when i turned it back on it was stuck on the apple logo. I googled it and realized I needed to restore in itunes. I tried it and it would get all the way to the end, and tell me it couldnt finish. If possible could anybody please give me step by step instructions on how to fix this problem. This is my only phone, and I would appreciate not having to buy another one, I dont have it like that, lol THANKS IN ADVANCE!

[xboxbml]

U dont unlock do u?...did u try DFU restore?...what baseband was it...