Minecraft, my RAM, modpacks, and FTB?

I use an HP Touchsmart 320 with 4
Gigs of ram. (I'm not sure what processor and whatnot) it was Windows 7. I tried to play FTB Infinity (161 mods) and it lagged badly on the home screen (single player, multiplayer screen) i managed to create a world and it took more than 10 mins to create a world and never loaded so i just closed minecraft. What should i do? I also used the Curse Launcher/Voice beta thing to launch the pack if that helps.

Your computer isn't powerful enough or you don't have that much ram left. You should use less mods or if you want to use that much mod buy more ram or buy a new computer for gaming.