Game crashes when starting up

I am trying to play on version 1.5.2 to play on a server hat won't be updating for a while.
I change my profile to the one set for 1.5.2 and start the game. It shows the Mojang logo screen for a few seconds and then just crashes.
It used to work just fine but one day it just stopped working.
I used to have mods in the .jar folder but I got rid of them and it still doesn't work.