Boot Problem After Replacing Rear Housing

Hi..

I'm hoping that someone can point me in the right direction.

Yesterday I replaced the rear housing on my 3G as the original had become very scratched..

I used the correct tools and followed a very indepth guide.

The only problem i now face is that my 3G will not boot unless it is pluged into the mains (I haven't tried it in iTunes yet)..

When it does boot from the mains it only boots for 7 seconds at a time and never gets passed the Apple logo..

When it is plugged in i can press the power button and it responds every time but only for 7 seconds and never gets passed the apple logo.. once unplugged it fails to boot when the power button is depressed

My main concern is that when i was extracting the batttery with the sponger it felt as if it had a slight crumble..

Is it a possibility that i damaged the battery..? Hense why it will not boot unless plugged in..

The only thing that doubts this in my mind is that if the battery was the problem the surely it would boot fully when plugged into the mains and not power off after 7 seconds..?

I'm a competent iPhone user and have managed to downgrade my own and friends firmwares etc and have been jailbreaking iphones for 2 years..

The replacing of the rear case was very straight forward..

Do you think it may be the battery or do you think its a logic board problem..?

Thanks

Thanks to those that looked.. Managed to sort it out, here's what i did incase you get the same problem..

Check all the ribbons.. Ribbon 3 was not correctly seated.. once this was fixed i had it back, apart from the screen was not lit correctly..

unplugged all ribbons and checked they were seated correctly..

Works fine now ;)