Wont let me restore after battery replacement. Turns on and off.

I just replaced the battery on my iPod touch 5th generation. Before assembling the iPod back together I wanted to test it out first. I pressed down on the power button a few times but nothing happened. Then I plugged it into charge. The apple logo kept appearing and disappearing. Then I plugged it into itunes. Same problem kept accruing. Which then I decided to put the iPod in DFU mode to restore it. The connect to iTunes icons came on and stayed on. iTunes downloaded the software and started the restore. As soon as it reached the "waiting for ipods response" the apple logo came back on the iPod. Giving me the same appearing and disappearing problem. iTunes gave me error code 21. Note: iPod only shows signs of life when plugged into power. So now I'm stuck with no progress. Im guessing my soldering was not done properly?

Any ideas would be much appreciated! Thank you :)