A while ago, my computer's motherboard failed. I decided that I'd build a new computer using the same memory and hard drive from my old computer. I ordered a new case, power supply, processor, graphics card, etc. and put it together. When I booted up the system, everything was working fine except for these little tiny dots all over my computer screen. When they are on a dark colored background, they appear red. When they're on a light colored background, they appear blue. They flicker sometimes, and when I scroll down really fast they appear all over the place. They're not just randomly all over the screen though, they seem to be in clumps. (Sorry if I didn't explain it very well.) I updated the graphics card's drivers and I tried reseating the graphics card but nothing worked.
I decided to try plugging my monitor into the onboard graphics, and only then did the dots go away. I'm pretty sure this means my graphics card was overheating, as the graphics card needs a minimum of 400 watts and my power supply is 400 watts. After doing a little research, I realized it's usually a good idea to get a power supply at least 100 watts above the recommended amount. Another thing it could be is that I ordered a new graphics card, but they gave me a refurbished one instead. Maybe the card itself was damaged or something.
So yeah, does anyone know what the problem is? Thanks. =)
(Here's a picture of the dots)