Have just replaced the battery in iPhone 3G.

Everything was straight forward except initial step of removing the screen. The gasket around the edge of the screen was pretty stretched and mangled when the screen was removed, possibly due to poor original assembly.

Reassembled phone without screen gasket (quite impossible to reinstall gasket) and with new battery but now when turned on the screen is blank with only the backlighting showing. iPhone still communicates with PC via iTunes. Have tried re-attaching the screen connectors a few times, but with same result.

I read a comment on the guide where someone had the same problem, but was able to fix it by restoring the factory settings for the phone. I tried this too, but it didn't work in my case.