I tried to upgrade my jailbroken iOS 4.3.3 to 4.3.5 (unjailbroken) using iTunes and received an error (I can't remember which one, I've been through numerous trials to fix it now) and now, no matter what, I receive unknown error 20 or 1. I've tried custom firmware, I've tried jailbreaking again, tried TinyUmbrella and nothing. I honestly can not figure this out and I truly need my phone. Is anyone able to troubleshoot me through this?

Scratch that. I fixed it somehow, I disabled all of my firewall/antivirus software and entered DFU once again, selected restore from the latest iTunes and it finally went through. Three straight hours and I finally have my iPhone working again. I probably should've done that first, I just didn't want to use more time than necessary (and I spent more time than I would've...) to get it working again. Anyway, thanks for being here guys, I honestly appreciate it. Although no one replied, I did get cumulative help from posts by other users. So, again, thank you guys and have a great iPhone 5 event day!

Good catch, A/V software (especially internet security software) can impact TCP/IP connectivity, and even though this uses USB to connect, it uses TCP/IP to transmit data. What specific A/V package were you using? That way if anyone searches on the forum for the name of it, they'll find this thread and be able to fix their issue as well.

Thanks!