iphone 3g in recovery mode

I have tried to reactivate my old 3g that has sat in a drawer last few years.
its in restore mode. I remember i had fiddled with the base band to enable tethering then later stupidly updated in iTunes to then result with restore mode.
I have tried Redsn0w (0.9.6rc8) on my mac, i have downloaded ipsw files 4.2.1. 8c148, (standard and custom) I have run the standard restore file then the custom in iTunes, it results in itunes saying" sorry can't help at this time" (or similar).
Am I using the wrong restore files? what should i do?

thanks for help