replaced screen and Lcd, now it wont turn on...

Hi

I have been repairing iphones for a little over a year now. Every once in a while I will repair a 3g screen and when I reassemble the phone will not come back on at all. Not even when I plug it in to charger or computer.

This has never happened to me with a 3gs nor has it happened with a 4, only on the 3g.

I am in hopes that other repair techs may have had this experience with the 3g and hopefully can help me trouble shoot...

Any help or suggestions would be appreciated