visual anomaly on start up screen

hello,

i have just noticed that when my computer boots up the screen at first shows half the image and then the full image, i am sure it never used to do this. please see attached(zipped) video.my computer is working fine, but i just want to know what could possibly be causing this problem.

thank you.

Could be a graphics problem there...? Might as well have your graphics card tested.

thank you,

i will, although everything else related to graphics is fine, its just this.