iPhone 4 - didn't work sound, does not work charging

Hi!

Recently I bought iPhone 4 on eBay, it had new dock connector but internal speaker and microphone didn't work. I decided to fix it bymyself but I faced a lot of problems...

First, the internal connector that wires main board and dock-speacker-home button group stoped working. I didn't damaged it, but when after my first try I put all together the home button didn't work. After 2-3 attempts I got everything (exepting sound) working. I plugged it to original "block" wall charger and left to fill up accumulator. But after 5 minutes charger blows up!

Why?!? It worked just now...

After that I tried to plug it to usb on my laptop - usb bus automaticly stoped working "because of possible damage". I tried to plug dock connector to USB byitself, unplugged from main board, no cirtuit, but as soon as I put everything together it stoped working again... But phone by itself worked fine before accumulator drained complitely

Guys, do you know, can you guess what could happen? Will changing dock connector solve the problem or... ? I can't understand what could happen, please, help!