Why won't my Cisco WRT54G2 router work?

My mom recently received a Cisco Linksys router from her boss, (model WRT54G2 V1.5) but when I tried to connect it to our computer at home it wouldn’t work correctly. I know it worked fine before her boss gave it to us, so I don’t think it’s defective. From what I can tell, I’ve done everything I’m supposed to do: the Ethernet cords are all hooked in the way they’re supposed to be, I reset everything to “factory defaults” and assigned a new SSID, password, and security key, the entire setup process went smoothly, I installed Network Magic, and all the LED lights on the router are blinking the way the User Guide says they should be. When I try to use the internet though, Network Magic says that I don’t have a connection. And it’s not just the wireless. I can’t even get a connection on my PC (I’m running Vista).

I’ve tried going to Network Magic many many times to troubleshoot the connection, and it actually does manage to fix the connection for all of five seconds. I can actually click on a link or two on my PC or get a wireless connection in these few seconds, but after that the connection just goes away. I thought it might be a firmware issue, but I’m not sure. I don’t think I would even be able to upgrade the firmware if I wanted to, since the router needs to be connected to the computer and actually working to do that. I don’t think it’s a firewall issue either, since I already checked that. I know it’s not a problem with my DSL box, because I’m using it at this very moment.

I’m not sure what’s wrong with my router, but if anyone has any advice, please leave an answer! Thank you!