I bought a new gaming PC but HDMI says "check signal cable" :(

Hello everyone! New member here with a big problem! 
I really hope your community can help me fix this! 
 

Long story short, I bought a PC 3 hours ago. Everything worked at the other place and then I plug it in my house... nothing happens! 
I've tried 3 other hdmi cables that works with other devices, Not working.
I've tried to plug que computer on another tv with hdmi. Not working.

I've tried to remove the SSD and the HDD, install new ones. Not working either.

I've unplugged my son's monitor... only to realise that my new computer doesn't take the "blue plug" type of thing.

I've ran out of solutions and I don't know what to do anymore! 
 

Could it be the resolution? If so, how do I change it when I can't see what I'm doing?
I'm lost.
 

Help, please!

Showing a photo of the side of the card isn't much use. Anyway the simplest solution is that the graphics card is not working, or the hdmi port on it anyway. You'll need a new one

It  could be it's the motherboard hdmi port used - try the HDMI port  on the graphic card instead. It should work then.

It's a common mistake.

Showing a photo of the side of the card isn't much use. Anyway the simplest solution is that the graphics card is not working, or the hdmi port on it anyway. You'll need a new one

Sounds like very bad advice. I said that the computer was working 15 minutes ago when I bought it. I've powered it on, checked the dxdiag to see if I was buying the thing as described, i unplugged it all, came back home and it wasn't working anymore. What you say is not a valable solution since I've mentioned that it worked on other tv / monitors.

It  could be it's the motherboard hdmi port used - try the HDMI port  on the graphic card instead. It should work then.

It's a common mistake.

Bless you! That was the problem! I used the wrong port! I didn't see the other hdmi ports loll they were blocked by a little plastic thing!
Thank you very much! 

**solved

You are very welcome!