i7 windows cubase problem lagging

my Samsung i7 Intel® Core™ i7-3630qm CPU @ 2.40 GHz is having trouble with Cubase Artist 6.0

when i am in production into 1 hour cubase starts to stutter , lag and has a hard time playing feedback, i usually have to pause and then replay,

i do not know whats the deal, this computer is a windows 8.1 , i7 ! :imp: