PCs tend to try and locate a working display very early on in the boot sequence, so they can show any problems. Should you normally use a fancy graphics card and that become unavailable, the system might revert to using less fancy circuitry on the system board. Does your system have a second display socket?
Because you have tried more than one monitor, we can rule that end out.
The other areas are the cable and the PC end.
Older PCs used "VGA" connectors, a D-shaped shell with 3 rows of pins/holes. If yours is one of these, examine the pins on the cable's plugs. It is not unknown for them to get bent when putting things back in a rush. I've straightened many of these with my needle-nosed pliers.
These days most PC to monitor cables have an HDMI plug at each end. Take it out and examine each end for damage. Take it somewhere brightly lit and use a magnifying glass. If it looks OK, plug it back in the other way round, because sometimes connectors make better contact in a different brand socket.
Once that has been ruled out, the PC is the next suspect, and its connector the most likely to fail. It will be more difficult to examine, but I have had good results using my phone camera with its flash. You can blow up the picture on screen to see details. The conductors are on either side of the "tongue" in the middle of the socket. If they are damaged, a good repair shop can solder in a replacement socket.
