How do I secure my linksys router?

I was unable to connect to the internet, so I reset my linksys router in an attempt to solve the issue. After doing so, I am now able to connect back to the internet using my connection. However, it now says "linksys" instead of my name and "unsecured network" instead of security-enabled network. I no longer have the box, cd nor instructions that came with the router, but i do have the security key if that helps. The model number is WRT54G2 V1. If someone can help with this issue, step by step instructions will be very much appreciated. Thank you!