Hot Air Expressed

I bought an AirPort Express last evening. Hurrah. But after a brief moment of detection (its presence was initially picked up by my G5 which has an Airport card), it could not be located again. This happened after the AirPort Express rebooted, which is how the installation process was supposed to work.
Up to this point, I was elated. Then I realised no sound was coming out from my stereo system. Then I noticed it was flashing orange, meaning it was no longer detecting any network.
A few complicating factors: Our D-Link wireless router was assigned the name ‘default’. Later on I realised another wireless network with the same name had been detected as well. It could have been another neighbour’s network – he could have just restarted his router or something.
So to be safe I renamed our network, renewed the lease on our wireless router (is that the right thing to do?), set my G5 to log on only to our newly-renamed network, and reset the Airport Express a couple of times, hoping to start again with the setup process. But it was still unable to connect to our network.
According to the manual (which I found barely useful as it only skimmed through all possibilities of connections), a steady green light meant the signal was picked up. It’s been perpetually flashing orange, which means there is no signal pickup, i.e. it is out of range.
But even when I plug it into a power socket literally INCHES away from my G5, or into another socket two feet below our D-Link router, it flashes orange! ‘Out of range’, my foot. And plugging a network cable into it at the same time doesn’t help either. At most, it glowed green for a few seconds, then went back to orange.
One possible theory is that my D-Link wireless router and the AirPort Express may have the same IP address, thereby causing some sort of conflict. I have no idea to find out if this is true.
I won’t have time to figure everything out until next week, so if anyone has any prior experience with this sort of problem, your advice would be deeply appreciated.