Ive just downloaded top gear polar mission in full 1080p

everytime i try to play it the sound is fine but the screen keeps freezing and then going again.

im running an fx60 at 2.8ghz with crossfired x1900s 2gb of ram so not sure if my system is up to it, i would have thought so but i downloaded blue planet in 1080p a while back and it did the same thing so i deleted it.

do u think its my system or something else

im using vlc player as its a .mkv file

also i checked task manager and mem usage is only 60mb but when the screen does run for a few seconds the cpu goes to 50%

do i need to make it use both cores(how?)

or do i need a different player

Could really do with your help

thanks