You should never take the phone apart yourself. Lesson in technology. Let the professionals handle that part!It might not be worth it anymore =(
RIP your iPhone 3G.
Seeing as it sounds like you took it apart, you might have done something wrong too so this could prevent it from operating properly.
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Yeah, there is no harm in trying if that's the case.I think with as many videos and websites online that step by step you through all repair process that anyone that has taken their phone in and it wasn't replaced should be able to and should do any and all repairs. They are easy to follow steps that aren't much more complicated than brushing your teeth. If Apple said they won't replace then there is no harm in trying.