New built pc, still my monitor says “no signal”.

Hello,

I just finished building a new pc yesterday, and everything was fine. All components were compatible, I was careful not to harm my motherboard and graphic card when I placed them in my case and I plugged everything in the right places. However, my monitor said “no signal” when I plugged in the hdmi cable into my pc. I was so tired after 7-8 hours of building, reading and researching that I weren’t very worried and I just tried several different things. One including plugging in my usb drive with windows 10 on. I think that was what ‘kickstartet’ The whole thing but since I was son tired, I’m not really sure. However, I had to move my pc into another room to plug in an Ethernet cable since I couldn’t reach from the router to my room. When I re-plugged everything, both my monitor and pc, I had the excact same problem with “no signal” showing up. I’ve done almost all the guides on YouTube, but since that’s solutions for problems regarding older pc’s it’s not working since I think my problem is a bit rare maybe? Anyone who can help me make it work again?
Timeline: no signal - signal and windows installed - no signal even though I didn’t changed anything