No network connection on a Mac G5 Powerbook (PC)

[Pilgrim]

I'm trying to troubleshoot my wife's older G5 PC which has a problem making an Internet connection.

Background:
1. When it was working, on boot she would get two 'security' prompts which needed to be "OK'd". Connection was then established.
2. Now, these prompts no longer appear.
3. Connection is via Cat 5 cable to a DSL wireless modem/router (Westell 7500)
4. Purchased and installed a PCI ethernet card which initially worked. This was done because the initial diagnosis was the MB ethernet was dead.
5. Again, no security prompts on boot and thus no connection can be established.
6. Ran through the connection "Wizard" with no results.
7. Modem recognizes the G5 (light is on for that connection) but cannot ping the machine from my PC over the LAN
8. Network "Preferences" shows no IP nor DNS information.
9. I plugged in the same Cat5 cable to her Macbook Pro laptop and it works fine.
10. She says on bootup there were about 5 security prompts (#5) which she had to "OK" and doing so allowed a connection. Those prompts no longer are displayed.

Not being familiar with MACs I really don't know how to go about resolving the issue. I suspect it is not hardware, but I could be wrong on that.

HELP!!