TV screen is pixelated when I try to use HDMI cord with my Macbook Pro.

I have a 15 inch early 2011 MacBook Pro with OS X El Capitan Version 10.11.1.

I've used an HDMI cord with my computer in the past and it was fine and it worked all the time. In October my computer started having display issues and I had to replace the logic board. Now my HDMI cord won't work. When it's plugged in my computer screen is normal, but the TV screen is pixelated and will not show what is actually on my computer screen. I don't know what the issue could be since I just got my computer fixed. My tv is a Samsung and it's the only I've always used when I use an HDMI cord. I'm trying to upload a picture of what the TV is doing but it isn't working.