You've probably done this already, but for the sake of all the people who come to this forum with problems similar to yours I'll chime in regardless.
95% of the time, problems like this are caused by the user turning something off, flicking some switch or another oftentimes by accident and then
either not noticing or forgetting about it later. Then when they go to use their system again and see that something is not working correctly, they panic.
PC parts don't generally just "break" on their own without outside influence, and I doubt that this is what happened to your system. So, if that
describes how you felt when you found your display not working, then calm down first and foremost. Now, you said that you've already checked to make
sure that everything is plugged in, seated properly and powered on, but do so again.
It won't hurt to double check, and in addition to that you didn't mention checking your monitor. It could be just as simple as that. Happy gaming, and I hope
you get your system fixed ASAP. Oh and also, if it turns out that it isn't just a matter of a flicked switch or unconnected cable and whatnot, it would be massively
helpful if you were to post your full system specs. I can't really help you personally beyond what I've already said, but there are people here on tom'sHARDWARE
that are far, far more knowledgeable than me in troubleshooting errors, and they would have a much easier time helping you fix your system if they knew what you
were working with.