Stuck at Building Terrain

Hi guys, I have searched around but haven't found a recent solution to this problem.
Two days ago Minecraft stopped loading or creating new worlds. It always get stuck at "Loading world, Building terrain".
I've tried uninstalling Minecraft, removing everything from %AppData%\Roaming\.minecraft, except for the saves directory. I uninstalled java, and so I have all the most recent versions of Minecraft, Java and of my video card driver. If I try to load any world, or even create a new one, java will use 100% CPU and Minecraft remains on Loading world Building Terrain.
I don't know what else to do. Please advice.

I have now tried to increase the JVM memory allocation, as per MC-23484. I tried 2G and then 4G, but still can't get it to work. I have no customization or game pack installed, just a clean Minecraft install.