Have you tried changing any of the settings? It might be using up too much memory. Or if you're using Forge (for legal mods I assume) then one of your mods might be conflicting with the startup of the game...
Ah, I don't use mods (very confusing lol) but I miight not have alot of memory, it does keep saying I have low memory.
Hmm... Try not to run too many programs at once. If all else fails, try allocating more RAM to Minecraft in the launcher under your Profile Page. Since you're not using mods, this link should help you: http://www.minecraftforum.net/forums/support/unmodified-minecraft-client/tutorials-and-faqs/1871637-tutorial-allocate-more-memory-for-minecraft
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