Quote from Sjaelen »Yeah, we can totally help you without any information at all. Good one.
Here's what you do:
Delete .minecraft (the folder).
Start up the game, and it'll redownload the basic game.
Now get the mods you want, and make sure none of them conflict. (Like, two mods use the same b.class)
Delete any mod (the entire mod) that conflicts with another one.
Install them all exactly how it says.
If it still doesn't work, then you're not installing them right.