Unablle to put iPhone4 in DFU mode
I got my brothers iphone to use and upgraded to same to iOS 5.1 and set it up with my iCloud id. I am unable to jailbreak it, i know it is a tethered jailbreak using Redsn0w. I have jailbroken lot of iphone before and even iPad's but when i try this i am unable to pu the iPhone in DFU mode, the screen stays black but Redsn0w says there No iPhone detected, follow instructions....
Can someone tell me if there is a problem or an alternate way to do this ?