Iphone baseband problems and restore?

Hi guys i have a huge problem. I have an iphone 3g 4.2.1. I hacked it earlier with redsn0w and unlocked cuz i have tmobile. Well i selected in redsn0w and ipad baseband to unlock it. So it all works out fine and when i finish i test out my multitasking while im waiting for my iphone to search fot tmobile. When i opened an app and then multitasked to another one it put me on safe mode. So tryed to repeat the process without multitasking but i need to restore it first right. So i tryed to restored and i got an error problem. I need to restore my iphone an order to use it but i cant restore it. On my iphone im stuck at a picture with the itunes symbol and the cable. Can anyone plz help me. Ive looked online and they said i have to use a custom firmware. But it would be a lot easire on my part if u guys can give me a step by step guide to fix this? PLZ I NEED HELP