Minecraft mods aren't working?

I'm playing minecraft 1.6.4 and I have optifine and carpenters blocks on the game already. Both work fine. I was building some thing and wanted something that came from a different mod, so I put that mod in my folder (already downloaded it, it worked fine before), but it won't show up. At all. I'm using some of the Life in the Woods pack stuff, like the dynamic lights and weapons mod, but those won't show up in game. The game runs fine, but the game won't show the mods I put in the mods folder. Anyone have an answer?