Mobs Froze

Mobs pasive and agresive are frozen after certan time of beaing around. Thier graphic is stuck in place while they still wonder around. My friend was with me on and for him all was good and sound while for me they all stuck.
All troubleshooting for repair game was made with assistance of Microsoft workers thru chat. (reinstal/update sytem/card driver update)
And they send me here.
So...
Hi. o/