Monitor display stuttering/flickering !!!

i tried putting in a pci card with the system on, i got a message

"network cable unplugged" and after that i was not able to fix that

network port no matter what(integrated with motherboard)

i put in a pci to lan card and am using it now and is working

properly.....

but now the problem is my display. the screen stutters when i try to

play videos and my cpu performane is way higher than before

these thing i already tried 1)re install driver, update driver 2) re

install OS 3)change frame rate 4)try different hard disk

stuttering started right after the ethernet port had problem