Sorry for not being able to determine the exact problem of yours, but in general when your system is getting locked up it’s due to the thermal sensor sending a critical overload signal to the notebook core system (on the sidenote, same applies to the desktops as well). You might want to track your performance with something like HWmonitor to figure if this is the issue. Normally it’s not a big deal to fix the hardware problem causing the overheating, you just have to be careful with cleaning, or refreshing the thermal paste.