Why is my iPhone not restoring?

I plugged my phone in after having a dead battery. First up, my iPhone decided to do that thing where it flashing the startup screen (apple logo) and flashing to a black screen over and over and over... So I googled around for some answers and finally came to the conclusion that I must put my phone into recovery mode and restore the whole thing (What a pain!). I proceeded to do so and was shortly presented with an error. It was error 21 which is a hardware problem. I tried different USB cables, different USB ports... Even different laptops to which I was still presented with this error. I then tried to restore in DFU mode and was presented with the same error. My last resort would be to go to a shop but I'm trying hard not to do so. My phone does nothing when off charge now and when on charge (whether it's connected to a wall or laptop) it shows the "Connect to iTunes" screen. Please help me, any solutions are welcome.