will load world short distance

hello
when i open a world, starting a new one, or loading an old one the world will load for a short distance and then the cursor pointer appears at the centre of the screen. when moved about it only stays visible inside a rectangular space, which is not defined by any lines. upon pressing keys nothing happens, but after clicking with the mouse, in a short period of time, the game will do whatever the keys you had pressed are supposed to do and then it closes. on the development console (in the launcher) it says:
Client> 2013-06-26 15:31:12 [SERVER] [WARNING] Can't keep up! Did the system time change, or is the server overloaded?
i dont know if this is a crash or not