Have you done all the obvious checks, e.g. tried a different PC, a different display cable, a different video port (e.g. VGA, HDMI instead of DVI) on the monitor itself? Sometimes the circuit for "HDMI" breaks, but the circuit for "VGA" is still working. Do both your video ports on your graphics card work, e.g. tested to another monitor?

Assuming you have done all the above, and you have no manual, you could open up the monitor case, and hunt around for burnt-out components (e.g. burn-marks on the circuit boards) or see if any of the electrolytic capacitors has expanded.

Electrolytic capacitors from Japan are usually very good, but other countries don't make them as well, and they may dry-out in a few years and then expand and stop working. Replacing a swollen capacitor with a new one with the same capacitance, voltage specs might restore the broken circuit.

Other than that, time to go hunting for a replacement (maybe secondhand) monitor.