Both multiplayer and single player crashes on me. I can't open up my worlds. I'm able to log in to minecraft, but when I click on a server and try going on it, it crashes. I think it may be the new single player commands for 1.4.2, but I'm not really sure because it started crashing when I added that onto my minecraft. Nevermind, I fixed it. Now the problem I'm having is that I can't place blocks or open chest, furnace, dispensers, and doors. Is there a way to fix that so I can place items and etc? Note: I can't place blocks on both single player and multiplayer. Nevermind again. I solved it myself.