Game Freezes

Recently, I completely removed Minecraft from my computer and then reinstalled it to start over from vanilla. This was due to a conflict with mods. This is the first time I've played, however, since 1.4.2. The only thing I kept from then was one of my save files that I really didn't want to lose. I started it up and everything went smoothly until I started destroying blocks. This caused my game to completely freeze up and I had to bring up the Task Manager to exit the game. Is this something I can fix? Or is this a bug? Maybe related to my previous save?