iPhone won't turn on

So my iphone 3g was working fine apart from the battery ran out very quickly. So I tried a DIY battery replacement. Once I'd put the phone back together everything was working properly. I then did a test call and realised nobody could hear me and I couldn't hear them so i figured the microphone and audio piece needed replacing/repairing. I opened the phone back up to have a quick look if all the cables looked ok. cable 3 wasn't in the correct place so after doing this I put it in and put the phone together again. I turned it back on and it was still in the same condition (all working ok apart from the mic and audio piece) So again i went to look inside, put it together again and now it wont even turn on!! does anyone know what this may be? I hope someone can help :)