hi, i've been a pair of days trying to jailbreak my iphone 4 3.1 gsm.updated to 6.1.3 with iTunes.
First i tried downgrading to 5.0.1 (that was the only firmware that worked after trying 6.1.2, 6.0, 5.1.1, etc) but after jailbreaking it it turned off suddenly and was impossible to make it...