No signal to monitor, PC does boot up.

Hi,

So I recently build a semi-new PC. It worked for a couple of weeks, then suddenly started going into a reboot loop, not getting past the BIOS. I brought it to a local computer/repair shop, they tested the system and all of its components, claiming my brand new motherboard was dead.

When I returned home with my supposedly dead PC I tried to turn it on. I heard it wasn't making the reboot loops anymore so I opened up my case, and noticed that they didn't plug the GPU onto the PSU. I turned off the power, unplugged my power cord and replugged my GPU, and then replugged everything back, turned on the power. Ta-da, it worked again, somewhat. I had to reset the BIOS and reconfigured everything, but it worked.

So the day after, that is today, I started testing some games and putting some rather big working loads onto the PC. I noticed that it started to get really hot, really quickly. I quickly noticed that the computer shop guys also forgot to plug the case fans to the PSU. So I turned off everything again, unplugged the power cord, replugged the case fans, etc. I had to shove some cables aside as it's a small Mini ITX case. I then tried to turn it on again, and so it did, everything sounds good, but my monitor doesn't show anything but a message saying that it's receiving no signal.

So I've tried resetting the CMOS BIOS thing again with the jumper and the battery. I've tested my PC using a different GPU. Is there anything else I can do?

I doubt anything is failing hardware wise.

Thanks in advance.