I downloaded a map and it crashed whilst loading multiple times. I deleted it and went onto my creative mode world, at that also crashed on startup multiple times. I don't know what to do.

My Minecraft (1.7.4 Unmodded) continues to crash while starting ANY of my singleplayer worlds. I recently downloaded an Earth map of Minecraft, and it crashed multiple times during the loading process. I then deleted it from my saves, and played on my creative mode world. That world proceeded to crash on startup as well (multiple times). I'm on a Windows 7 laptop and I have the latest version of Java. I began trying to play on a server, and it also crashed on startup. I can't play Minecraft anymore 😞