Try opening your browser and go to 192.168.0.1 or 192.168.1.1. You can try that and see if it lets you in.
If it asks you for a password you can try leaving it blank and if it asks for a username try admin.
Look at the bottom of your router and it may tell you the default password.
When you get in if you can look a round for WEP security or and type of security like that. Type a password in and save it and write it down somewhere so you remember it or you will have to change it again.