dark background

Hey, I have a problem with my monitor. When there are dark colours on my screen and they move (for example a dark window where you scroll up and down) the dark colours seem to fade a bit. I made a video to try to show what I mean but you can't see it really well. At 0:05 you can see it the best...

I'm about to buy windows 10 and to install it of course but my problem is that I had some issues with my PC . By that I mean it won't boot up correctly so instead of reinstalling win8 I decided to go and buy win10 cause why not... And I'm actually asking...will I need to format my HDD/disk...