iPhone 4 seems to be bricked after iOS 6.1.2 update. Help?

Hey Everyone.

So, a couple weeks ago, I updated my iPhone 4 (currently have the 5) to iOS 6.1.2 over-the-air. A day after that, the phone would not turn on at all. No response to anything. However, when I plug it into the wall, the apple logo shows for a couple seconds, then a black screen. This repeats itself until I unplug the phone. BUT, when I put it on the dock on my alarm clock, it shows iOS 6 with the slide to unlock, but when I do it tells me to connect to iTunes. And, it says the phone has 100% battery life. As you can see, this is really weird. So, I connect the phone to iTunes, and the connect to iTunes logo shows up on my phone. When I try to restore, I run into many errors, the 2 most common being 21 and 2001.

My dad's iPhone 4 broke so if I get this fixed I am going to use it and give my dad the 5 as he needs a good phone for his business.

Hopefully you guys can help me out!

-Sammy D