WEP can be cracked easily enough if someone wanted, there loads of tutorial vids about this out there, but probably not this here, really looks like it lost its settings which happened me once.
who's your ISP? Ive got that 54g as well, its a few minutes admin to reset the security info.
1. change the default password on the router,
2. set your wireless settings, use WPA.
3. Turn on firewall.
4. When you get on to web, download the latest firmware from linksys support site and install.