Minecraft Forge 1.6.4 not working?

I installed Minecraft Forge correctly, and when i open it without any mods in the mods folder, it works perfectly. But when I even add one (i tried three different mods) mod in the folder, it doesn't work. It opens, and shows the Mojang logo. Then it stops responding, and just crashes. There isn't even a crash report. Any help?

What I'm thinking is happening is some form of incompatibility, either with the mods you're using or Forge itself.

Either that, or the mod in question is too much for Minecraft or your computer to handle to run properly.

Try installing smaller mods to see if it's forge or not. If it continues to crash, re-install forge and try again.