I have an iphone 4, running 4.2.1 iOS, jailbreaked (tethered) with redsn0w. Everything was working fine, but I downloaded a Cydia app (iBlacklist) and the Springboard Crashed, and never rebooted (the pineapple logo was frozen into the screen, and nothing ever happened). I tried rebooting into tethered (redsn0w option) various times, but still nothing happened, it was bricked. I tried restoring with Apple, but I got error code 1013. I later tried jailbreaking it again and re-installing Cydia, and the installation froze at around 80%. Now I have a brick and I'm desperately looking for help.
I'm guessing you dont need to unlock. To restore without getting that 1013 error open tiny umbrella, click advanced deselect the option to set hosts to cydia on exit. Then close tiny umbrella and try restoring again.