In order for other people to join your "dedicated server". You need to give the people the IP Address that is "public" mentioned by Tebas. To find out what is your Public ip, go to www.whatismyip.com . You should see your IP listed on that page, Your IP Address is : xxx.xxx.xxx.xxx . With this IP, plus the port 27015 (default) forwarded to the LAN IP of yours ( 192.168.1.??? depending on your server machine ) . There should be no problem at all.

As for your problem of invalid password for the router. You might be using the wrong default password, what is your Router brand/model? Different brand have different username or password. They could be admin for username and password for password. Or in worst case scenario, someone changed your router password. So you cant access it with the default 1.. But you can reset the whole router ( there should be a small hole at the back of the router, poke it with a pin or something while it is on. Everything should be reseted including your broadband account informations, so beware..

Good Luck