How can I fix an Iphone 4 booting in the restore

I've restored my Iphone 4 and wanted to sell it so I stayed it in the initials conditions to another person set when buy it. After some days I turned on and the Iphone just looping in the apple logo, so I started it in the recovery mode that show the cable and Itunes logo and tryed to restore at Itunes, but when the restore starts the Iphone boot and came back to looping again. I tryed the same proceeding in DFU mode and happened the same. I tryed to restore by redsnow and the same happened and after starts the looping the redsnow shows a message "Coulnd't upload ibss". I tryed to downgrade to 5.1.1 but I don't have the SHSH. I think the main problem is that when the installation of IOS starts the iphone boot and interrupt the restore. P.S.: The iphone is a factory unlocked. I'm from Brazil What can I do to fix it? Thanks