I have been playing COD4 with no problems until yesterday. Now when I try to play online on the PS3, it won't let me join any games. It shows my name and my rank, but no other users in any rooms to play. What can I be doing wrong?

It will put you in a room on your own when it cannot find a game for you. Sometimes waiting for a while in that room will work and players will join. But its a connection issue for sure if it keeps on doing the same thing.

If you havent already, try searching multiple game types, Ground war and Headquarters are usually the most popular modes so you have a better chance of finding a good room with these.

i have same problem but its first time playing online so i dont have those things i only have free for all team deathmatch and 1 other thing but it sits there searching but nothing happens.

Hmm thats strange, sometimes your account can get screwed up if u quit a join and then rejoin. Other than that sometimes if u are in a party that has just been disbanded you need to go back to the opening screen then go to multiplayer again for it to work.