Spongebob Squarepants: Battle for Bikini bottom cheat codes?

Okay, I've looked up what the cheat codes are and I know a few, but I can't punch them in. The L+R isn't working and after I put the buttons in I never hear a noise to see if it works. I'm having trouble accessing the cheat codes. HELP! I can't defeat the stupid Kah-Rah-Tae!